Patent Publication Number: US-9895097-B2

Title: Systems and methods for delivering bone conduction stimuli to and for measuring gravitation receptor functions of the inner ear

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. patent application Ser. No. 14/276,939, filed May 13, 2014, and titled “SYSTEMS AND METHODS FOR DELIVERING BONE CONDUCTION STIMULI TO AND FOR MEASURING GRAVITATION RECEPTOR FUNCTIONS OF THE INNER EAR,” which claims priority to U.S. Provisional Patent Application No. 61/822,694, filed May 13, 2013, and titled “APPARATUS AND METHOD FOR DELIVERING BONE-CONDUCTION STIMULI TO AND FOR MEASURING GRAVITATION RECEPTOR FUNCTIONS OF THE INNER EAR,” which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to systems and methods for testing the inner ear, and more particularly, to systems and methods for delivering bone conduction stimuli to and for measuring gravitation receptor functions of the inner ear. 
     BACKGROUND 
     The inner ear is the innermost part of the ear. As shown in  FIGS. 1A and 1B , sound is directed by the pinna  102  through the ear canal  104  to the eardrum  106 . The eardrum  106  moves the bones of the middle ear  108  to vibrate the cochlea. The cochlea generates electric pulses that are correlated with the sound, and these electric pulses are sent to the brain. The inner ear further includes a balance sensing system  110 , referred to as the vestibular system. The vestibular system  110  generally includes three semicircular canals  112  and two pairs of otolithic organs (each located on a different side of the head). Each pair of otolithic organs includes a utricle  116  and a saccule  118 . Internal to the semicircular canals  112  and surrounding the otolithic organs are the endolymphatic ducts containing endolymph. Multiple ampullae  120  may also be disposed in the inner ear. The semicircular canals  112  may be characterized as providing three rotational receptors (the ampullae  120 ) and two gravitational receptors (the otolithic organs  116 ,  118 ). The semicircular canals  112  and the otolithic organs  116 ,  118  in the inner ear contain hair-cell transduction mechanisms that, for example, help (i) provide the brain with spatial orientation cues, (ii) keep the eyes focused on a target when the head is in motion, and (iii) maintain balance. Specifically, the ampullae  120  of the semicircular canal  112  respond to rotations, while the otolithic organs  116 ,  118  sense linear accelerations, decelerations, and tilting. As a result, stimulations of normal otolithic organs, specifically, the utricle  116  and saccule  118 , will produce a response in (i) the eye muscles to allow the eyes to maintain gaze and (ii) the muscles that contribute to movement of the head. 
     Gravitational receptor asymmetry produces dizziness, a sense of motion, tilting, being pushed, pulled or falling; while rotational receptor asymmetry produces true rotational vertigo. Ninety million Americans go to health care providers because of vertigo, dizziness, or balance problems. It is the second most common complaint heard in doctor&#39;s offices, and will occur in 70% of the nation&#39;s population at some time in their lives. Falls account for 50% of accidental deaths in the elderly, and 10% of falls result in hospitalization. Every 15 seconds, an older adult is treated in the emergency room for a fall; every 29 minutes, an adult dies following a fall. Research has indicated that the annual direct and indirect costs of fall-related injuries are estimated to reach $54.9 billion by the year 2020, and that participants with vestibular dysfunction who were symptomatic, i.e., reported dizziness, independently increased the odds of falling more than 12-fold. Research has also indicated that increasing age is associated with an increased prevalence of vestibular dysfunction. There are also military considerations with post combat-induced injuries and loss of military aircraft and other assets that contribute to the scope of vestibular related problems. 
     It is known that bone-conducted stimulation to the head, as well as auditory stimulation, excites the otolithic organs  116 ,  118 . As a result of the stimulation, a response (e.g., an action potential and/or an attendant movement) is produced at the sternocleidomastoid muscle (a neck muscle that contributes to the movement of the head) and the extraocular muscles (eye muscles that allow the eyes to move). In addition, inhibitory or excitatory action potentials and/or attendant movements are produced at other muscles (e.g., triceps, splenius capitus, or inferior oblique muscles) in response to activation of the two otolithic organs. A muscle response may be characterized or measured as an electrical impulse from the brain to the muscles, and/or as an attendant movement of one or both eyes (e.g., a rotation of the globe, referred to as “torsional rotation”). Specifically, a cervical vestibular evoked myogenic potential (cVEMP) response has been observed to be an inhibitory response, measured at the sternocleidomastoid muscle, corresponding to an activation of the saccule  118 . Also, an ocular vestibular evoked myogenic potential (oVEMP) response has been observed to be an excitatory response, measured at the inferior oblique muscle (an extraocular muscle that controls a specific movement of the eyes), corresponding to an activation of the utricle  116 . Another excitatory ocular response corresponding to an activation of the utricle  116 , and the consequent activity of the inferior oblique muscle of the eye, is ocular motion (e.g., torsional movement of the eye). This movement may be measured by visually monitoring a patient&#39;s eye(s) using a video or other image capture system; this response may be referred to herein as an “oculometric” response. The extraocular muscles include six muscles, including the inferior oblique, superior oblique, medial rectus, superior rectus, inferior rectus, and the lateral rectus muscles. By observing the cVEMP, oVEMP, and/or oculometric response, diseases, disorders, and conditions affecting the vestibular system and the balance sensing system of a person may be observed. 
     Besides producing auditory stimuli, some in the art have developed various types of apparatus to deliver bone conduction stimuli to certain parts of the skull bone (e.g., the frontal bone, the parietal bone, the occipital bone) to test the gravitational receptor functions of the inner ear. For example, some in the art have employed electromechanical devices and mini-shaker apparatus. Such apparatus have been observed to produce stimuli of insufficient magnitude to elicit a robust response. Some in the art have also employed solenoid actuators. Existing arrangements including solenoid actuators may produce stimuli of sufficient magnitude, but may also produce other stimulations of the otolithic organs for certain patients. Some have used reflex hammers. Of these conventional approaches, the reflex hammer tapping of the forehead may produce the most robust cVEMP, oVEMP, and/or oculometric responses, but there is no mechanism to standardize and calibrate the stimulus. 
     Bone conduction stimulus may be applied at various locations on the head, for example, at the front of the forehead along the mid line.  FIGS. 1C and 1D  illustrate example electrode placement diagrams for delivery of bone conduction stimuli. The bone conduction stimuli may be applied at the same location among different patients and among different tests in order to improve the repeatability of the testing, for example, at the “Fz” location  120 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features of embodiments will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  illustrate various anatomical structures associated with the human ear and inner ear; 
         FIGS. 1C and 1D  illustrate example electrode placement diagrams for delivery of bone conduction stimuli; 
         FIG. 2  illustrates a system for measuring gravitational receptor functions of the inner ear, according to various embodiments; 
         FIG. 3  illustrates an electrically driven actuator, according to various embodiments; 
         FIGS. 4A-4G  illustrate various embodiments of the electrically driven actuator of  FIG. 3 ; 
         FIGS. 5A and 5B  illustrate a handheld electrically driven actuator, according to various embodiments; 
         FIGS. 6A-6B  illustrate electrically driven actuators, according to various embodiments; 
         FIGS. 7A-7D  illustrate example testing sequences for measuring gravitation receptor functions, according to various embodiments; 
         FIGS. 7E-7G  show example outputs of a test employing one of the testing sequences illustrated in  FIGS. 7A-7D , according to various embodiments; 
         FIG. 8  illustrates an apparatus for measuring ocular vestibular evoked myogenic potential (oVEMP) response, according to various embodiments; 
         FIG. 9  illustrates an apparatus for measuring oVEMP response, according to various embodiments; 
         FIGS. 10A-10C  illustrate several views of an apparatus for measuring both cervical vestibular evoked myogenic potential (cVEMP) and oVEMP responses, according to various embodiments; 
         FIG. 11  illustrates an apparatus for measuring patient response, according to various embodiments; 
         FIGS. 12A-12C  illustrate a graphical user interface for viewing patient responses, according to various embodiments; and 
         FIGS. 13A-13C  illustrate a handheld electrically driven actuator, according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “gravitation receptor functions” may refer to operations of the vestibular system, such as the provision of perception and monitoring of gravity, acceleration, deceleration, orientation, balance, and movement. The term may also refer to physiological response resulting from the stimulation of the vestibular system, such as the cervical vestibular evoked myogenic potential (cVEMP), the ocular vestibular evoked myogenic potential (oVEMP), or an oculometric response. 
     As used herein, the term “stimuli” may refer to a series of distinct forces or impulses applied to a person to measure or test the gravitation receptor functions of the person&#39;s inner ear. Each force may be generated by a mechanical impact applied to the skull bone of a person (e.g., a patient) and may be conducted through the skull bone to the inner ear to elicit a physiological response of the person&#39;s vestibular system. A subset of a stimuli having only one force is a stimulus. 
     As used herein, the term “patient” may refer to any person who is receiving a bone conduction stimulus or is being measured for the gravitation receptor functions of his or her inner ear. 
     As used herein, the term “cervical vestibular evoked myogenic potential,” abbreviated as “cVEMP,” may refer to an inhibitory response measured at the sternocleidomastoid muscle, corresponding to activations of the saccule. 
     As used herein, the term “ocular vestibular evoked myogenic potential,” abbreviated as “oVEMP,” may refer to an excitatory response measured at the extraocular muscle (e.g., the inferior oblique muscle), corresponding to activation of the utricle. 
     As used herein, the term “oculometric response” may refer to an excitatotry response measured by visually monitoring the movement of a patient&#39;s eye (e.g., for torsional or other relevant motions). 
     As used herein, the term “physiological response” may refer to cVEMP, oVEMP, and/or oculometric response. 
     As used herein, the term “skull bone” may refer to a subset of bones of the head including the frontal bone, the parietal bone, and the occipital bone. 
     In an exemplary embodiment, a method and apparatus may provide a stimulus to the skull bone in a manner that does not contaminate, or interfere with, a measurement of the resulting physiological response of the person&#39;s vestibular system (i.e., gravitational receptor functions). To provide such a measurement, the stimulus may be generated in a manner so as to not produce an auditory response of the ear. Herein, various embodiments of the present disclosure recognize that bone conduction stimulation (performed without auditory stimulation) may produce a more robust response of the gravitation receptor in the inner ear relative to the conventional noise-masking and noise-normalizing techniques known in the art. In particular, various embodiments of the present disclosure recognize that stimulation of the auditory system may produce a response of the gravitation receptor in the inner ear, which may interfere with and/or contaminate the response from bone conduction stimulation. This stimulation of the auditory system may be referred to as “air-conduction stimulation” and is the result of sound waves (i.e., an “air-conduction” stimulus) that stimulates the eardrum, rather than a force generated by a mechanical impact to the skull bone that is conducted through the skull bone to the inner ear. To avoid triggering an auditory response of the ear during bone conduction stimulation, embodiments of the apparatuses disclosed herein may operate in a generally silent manner. In addition to being substantially silent, various embodiments may be configured to deliver more impacts (up to 500% more relative to systems known in the art) at scalable impact intensity, enabling higher fidelity measurements than previously achievable. Thus embodiments disclosed herein may be advantageous for testing the human balance sensing receptors in the inner ear, and more particularly, to testing otolithic responses. 
     Various embodiments of the apparatuses disclosed herein may be portable and may be configured for fast deployment. In field testing, it has been observed that various embodiments of the apparatus may be administered faster than traditional acoustic physiological response systems. In addition to providing substantially interference-free or contamination-free measurement, various embodiments may sufficiently saturate the gravitational receptor so that inter-aural differences are more accurate and consistent, thereby reducing variability among tests. Such saturation has been described in P. A. Wackym et al.,  Rapid cVEMP and oVEMP Responses Elicited by a Novel Head Striker and Recording Device,  33 O TOL . N EUROTOL.  1392-1400 (2012), which is incorporated by reference herein in its entirety. 
     In some embodiments, the methods and apparatuses disclosed herein may provide for consistent and quickly deployable measuring of physiological response. Specifically, various embodiments may be deployed for a measurement (or series thereof) in less time relative to conventional protocols. 
     In one aspect, a method and apparatus may provide for consistent and quickly deployable measuring of action potential of the extraocular muscles (e.g., oVEMP). To enable such a measurement, the apparatus may be adapted to be quickly and easily seated (like a mask) over at least a portion of a patient&#39;s face. An electrode (or plurality thereof) may extend from the apparatus and may be situated over at least a portion of the extraocular muscle of at least one eye. In some embodiments, other sensors (e.g., accelerometers) may be coupled to the apparatus and may provide data useful for normalization and/or feedback, as discussed below. The apparatus and electrode may not impinge on the globe of the eye or the extraocular muscle nor limit motions of the globe, and thus may provide for a clearer and more robust measurement of the oVEMP response than conventional approaches. 
     In another aspect, a method and apparatus may provide for consistent and quickly deployable measuring of oculometric responses. To enable such a measurement, the apparatus including an image capture device (e.g., a video camera) may be adapted to be quickly positioned to image at least a portion of a patient&#39;s face, including one or more of the patient&#39;s eyes. Images may be captured at any suitable frequency (e.g., 100 Hertz). In some embodiments, other sensors (e.g., accelerometers and/or electrodes) may be coupled to the apparatus and may provide data useful for normalization and/or feedback. The apparatus may not impinge on the globe of the eye or the extraocular muscle nor limit motions of the globe, and thus may provide for a clearer and more robust measurement of the oculometric response than conventional approaches. 
     In another aspect, a method and apparatus may provide for consistent and quickly deployable measuring of action potentials of the sternocleidomastoid muscles (e.g., cVEMP). To enable such a measurement, the apparatus may provide a resting area for the patient&#39;s chin while causing the patient to lean (i.e., tilt or bend) forward. In doing so, the apparatus may cause the patient to flex his or her neck in a manner that causes a portion of the sternocleidomastoid muscles to contract. The cVEMP response is an inhibitory response, and thus the sternocleidomastoid muscles should be contracted during the measuring or testing to detect the inhibition. By providing assistance and/or support to reduce strain during the measurement, particularly for certain patients (i.e., impaired or injured), such embodiments may enable robust and consistent measurements. 
     Existing protocols typically require the patient to lie supine while flexing his or her neck and turning his or her head against resistance. For certain patients (e.g., elderly patients, or patients suffering from kyphosis), this protocol may be more than uncomfortable. Such patients may not have the physical stamina to maintain the suspension and flexion of their neck for the duration of the testing or measurement. Additionally, such protocols may aggravate ailments, such as temporomandibular joint dysfunction, due to the excessive force applied to the joint while the patient is turning his or her head against resistance. The present embodiment alleviates such strain and provides the patient with a more comfortable testing position by allowing contraction of the sternocleidomastoid muscles without straining the temporomandibular joint and/or neck and spine. 
     In another exemplary embodiment, a method and system may provide for novel measurement schemes, such as measurement of an input-output function of the gravitational receptor functions as well as measurements with normalized responses. A normalized-response measurement may be advantageously employed in a clinical or research protocol to determine subtle defects of the gravitational receptors and differences thereof. The input-output function of the gravitational receptors has not been previously studied. These apparatus may also provide capabilities for more frequent stimuli-delivery than achievable with conventional approaches. 
       FIG. 2  illustrates a system  200  for measuring gravitational receptor functions of the inner ear, according to various embodiments. The system  200  may include an electrically driven actuator  202  (shown as “actuator  202 ”) to deliver a bone conduction stimulus  203  (or a sequence thereof) to a location  216  of the head of the patient  201  and thus to the skull bone of a patient  201 . The system  200  may include a controller  204  to actuate the electrically driven actuator  202 . In some embodiments, the controller  204  and the electrically driven actuator  202  may form an electrically driven actuator system. In some embodiments, the electrically driven actuator system may further include the interface unit  210  (discussed below). The electrically driven actuator  202  may be adapted to deliver the bone conduction stimulus  203  in a manner that substantially only induces bone-conducted stimulation and does not induce a substantial auditory stimulation. The auditory stimulation may be of a negligible magnitude so as to not contaminate or interfere with the measured response resulting from the bone conduction stimulation. As such, the electrically driven actuator  202  may operate in a generally silent manner as compared to conventional actuator arrangements used in the art (e.g., conventional solenoid actuator arrangements) while sufficiently saturating the gravitational receptor for more consistent measurement between different impacts and/or tests. In particular, conventional solenoid actuator arrangements have been observed to produce sound in the range of 70-80 decibels Hearing Level (dB HL). The electrically driven actuator  202  may produce a sound level between 29.2 dB HL and 50 dB HL, a substantial reduction. Noise suppressing earplugs and/or ear covers may be additionally employed to further reduce interference and contamination from auditory stimulation. As discussed herein, the electrically driven actuator  202  may also deliver stimuli more frequently than conventional solenoids, strengthening the ability to average the responses and reduce the impact of noise, and may also be configured to deliver scalable stimuli so that input-output functions can be calculated or activation thresholds (e.g., evoked potential thresholds; the amount of force and acceleration needed to achieve the maximal response) determined. 
     The controller  204  may be a computer system that operates measurement software configured to control the operation of the electrically driven actuator  202 . For example, the controller  204  may be part of an off-the-shelf data acquisition system, such as those manufactured by National Instruments, Inc. (Austin, Tex.). 
     The system  200  may include a plurality of sensors  206 . In some embodiments, one or more of the sensors  206  may be configured to measure a signal  207  corresponding to a response of the patient  201  to the bone conduction stimulus  203 . The measured signal  207  may be any representation of a signal corresponding to a physical phenomenon, including a pickup or sensed signal from an electrode or an image signal captured by an image capture device (e.g., a video camera), and/or including any conversion, digitization, transformation, and/or filtering performed by a signal processing circuitry and/or a data processor on a measured signal (e.g., as discussed below with reference to the interface unit  210 ). For example, in some embodiments in which the sensors  206  include electrodes, the interface unit  210  may include a linear current amplifier, which may reduce the output force variability by over 90% relative to standard switching amplifiers. In another example, in some embodiments in which the sensors  206  include one or more video cameras, the interface unit  210  may include signal processing circuitry for filtering, noise removal, landmark tracking (e.g., pupil tracking), and any other processing operations typically performed by conventional eye movement tracking systems (such as characterization of the direction, speed, and/or magnitude of horizontal, vertical, and/or torsional eye movements as a function of time, and/or changes in pupil size over time). In another example, the measured signal may be processed by a low-pass filter to remove or attenuate frequency content above a cut-off frequency (e.g., 50 Hertz). In some embodiments, the low-pass filter may include a Bessel filter, which provides an analog linear filter with a maximally flat group/phase delay (i.e., a maximally linear phase response) to preserve the wave shape of filtered signals in the passband. 
     Any of the signals transmitted between different components of the system  200  may be transmitted via a wired or wireless communication channel. In some embodiments, wireless communication may take place using a short-range wireless communication protocol, such as Bluetooth. 
     In some embodiments, one or more of the plurality of sensors  206  may be configured to seat over a portion of the extraocular muscle of at least one eye and/or a portion of one of the sternocleidomastoid muscles. In some embodiments, the measured signal  207  may correspond to an action potential of at least one of the muscles when that at least one muscle responds to the bone-conducting stimulus and/or stimuli. In some embodiments, the sensors  206  may be included in a mask  209  adapted to seat over at least a portion of the face of the patient  201 . The sensors  206  may include one or more preamplified electrodes. An example of a surface preamplified electrode that may be included in the sensors  206  is the Z03 EMG preamplified electrode manufactured by Motion Lab Systems, Inc. (Baton Rouge, La.). In some applications, preamplified reusable electrodes may present challenges due to picking up additional electrical artifact. In such applications, the use of disposable electrodes and increased signal amplification before data is logged may remedy the issue. 
     An example of a mask  209  that may be adapted to include the sensors  206  is the Model No. 1720xxxx eye protector manufactured by BSN Sports (Dallas, Tex.). Another example of a mask  209  may be adapted from computer assisted designs and custom 3D printing. In some embodiments, the sensors  206  may be mounted on an articulating arm. An example of a suitable articulating arm may include positioners, such as the Part No. PPM100 articulating arm manufactured by Tektronix, Inc. (Beaverton, Oreg.). An articulating arm may be coupled to a base and provide at least three-axis freedom of movement. Various types of articulating arms may be employed, which may be manually operated or computer-operated. Another example of an articulating arm on which the sensors  206  may be mounted in some embodiments is the Model No. 96130 arm manufactured by Moffatt Products, Inc. (Watertown, S. Dak.). 
     In some embodiments, one or more of the sensors  206  may capture images of movement of the eye. A measured signal  207  in such embodiments may correspond to one or more images of one or more of the patient&#39;s eyes. The sensors  206  may include any suitable image capture devices, such as a digital video camera, and may perform imaging using any suitable wavelength or wavelengths (e.g., visible light imaging and/or infrared light imaging). The sensors  206  may be mounted on tripods or any other suitable support frame and may be calibrated for alignment with desired landmarks on the patient&#39;s body (e.g., facial or eye features) in preparation for data collection. 
     In some embodiments, the sensors  206  may include one or more sensors configured to provide impact-related feedback to the interface unit  210  and the controller  204 . For example, the sensors  206  may include one or more accelerometers positioned on the head of the patient  201 . These accelerometers may be configured to detect the acceleration of the portions of the head proximate to the accelerometers, and transmit this acceleration data back to the controller  204  and/or the interface unit  210 . The controller  204  or the interface unit  210  may use the acceleration data to determine the forces experienced by the patient  201  during impact, in accordance with known physical principles. In some embodiments, the controller  204  or the interface unit  210  may use the acceleration data to normalize the response signal  207  (e.g., so that responses to higher force impacts can be properly compared to responses to lower force impacts). In some embodiments, the controller  204  may use the acceleration data to adjust subsequent impacts to achieve a desired force (e.g., in a feedback loop, as understood in the art). In some embodiments, one or more accelerometers may be mounted on each of the mastoid bones to generate data indicative of the force delivered to the temporal bone. 
     The system  200  may include a recorder  208  (shown as part of the controller  204 ) to receive the signal  207  from the sensors  206 . The sensors  206  may interface to the controller  204  via an interface unit  210 , which may include amplifiers and/or signal processing circuitry configured to process and/or enhance the measured signal  207 . The interface unit  210  may be a custom unit or a commercially available component. An example of the interface unit  210  that may be suitable for some embodiments is a multifunction data acquisition system (DAQ), such as the Model No. NI USB-6009 multifunction DAQ manufactured by National Instruments, Inc. (Austin, Tex.), which has, among other features, eight 14-bit analog-input channels that can each record 48,000 samples per second. The interface unit  210  may include buttons, knobs, display devices, and other user interface elements that may be operated and/or viewed by an operator of the system  200  to observe measurements made or change the characteristics of the stimuli delivered by the system  200 . For example, a knob or slider on the interface unit  210  may be coupled with the controller  204  so that rotations of the knob or translations of the slider may cause the force of the delivered stimuli to increase or decrease. 
     The system  200  may include a trigger  212  to initiate the electrically driven actuator  202  to deliver the bone conduction stimulus  203 . In an embodiment, the trigger  212  may be an electrical switch operatively mounted on the actuator  202 . The switch may be linked to the controller  204  to trigger a signal to the controller  204  when actuated. In addition to, or in lieu of, the trigger  212  operatively mounted on the actuator  202 , the trigger  212  may be a part of the user interface of the controller  204 . For example, the trigger  212  may include tangible buttons on a console or keypad or a graphically displayed button shown on a display  214 . In another embodiment, the trigger  212  may be part of a remote switch adapted to be actuated by an operator&#39;s extremity. The remote switch may be situated on the floor as a foot pedal or a table top as part of a hand console. As such, the trigger  212  may be operated by the operator&#39;s hand or foot. An operator may be any person who is conducting or assisting in the measuring or testing of the gravitation receptor function using the system  200 . In another embodiment, the trigger  212  may be part of a voice-recognition system having a microphone and voice-processing system to allow for voice-actuated triggering. Various voice-recognition system and voice-actuated triggering are generally known in the art and may be employed within various embodiments. The microphone may provide an audio signal to the voice-processing system. The voice-processing system may be part of the controller  204 . The voice-processing system may include a processor configured to analyze the audio signal to determine presence of a command corresponding to actuation of the trigger  212 . Upon determining that a voice command has been issued to trigger the actuation, the processor may cause a trigger signal to actuate the electrically driven actuator  202 . The trigger signal may be provided to the controller  204 . 
     In some embodiments, the system  200  may include a sensor disposed on or proximate to the electrically driven actuator  202  to output an electrical signal to the controller  204  when an impactor coupled to the electrically driven actuator  202  is proximal to the striking point. The electrical signal may be received by the controller  204  and may trigger a recording of an action potential at the patient  201  (e.g., the action potential corresponding to the gravitation receptors of an inner ear of the patient  201 ) and/or one or more images of the eyes of the patient  201  (e.g., to capture movement related to stimulation of the gravitation receptors of the inner ear of the patient  201 ). 
     The system  200  may include a display  214  to present the measured response. The display  214  may include capacitive or other tactile sensors, and thus may receive operator inputs (e.g., to select shapes and amplitudes of various waveforms, as discussed below). In some embodiments, the display  214  may receive control signals to display indicators of eye movement and/or action potentials. For example, a displayed eye movement indicator may include a graph of the direction of eye movement over time, a graph of the magnitude of eye movement over time (e.g., horizontal, vertical, or torsional), a graph of the change in pupil diameter over time, or any other visualization of raw or processed eye movement data. Other examples of various displays are discussed below. 
     The system  200  may be configured to allow for rapid field testing of both gravitation receptors in each inner ear. Each of the two gravitational receptors (i.e., the saccule and utricle) may be tested individually or simultaneously on one side. Alternatively, all four receptors may be tested simultaneously and bilaterally. Simultaneous testing may be employed for quantitative assessment, and bilateral testing may be employed for rapid bedside screening of peripheral gravitational receptor functions. As such, some or all of a cVEMP response, an oVEMP response, or an oculometric response, may be measured simultaneously, or in sequence, for one or both sides of the head. 
     In an illustrative embodiment, the actuator  202  may part of a handheld device, enclosed in a casing, to allow for easy manipulation and delivery of the bone conduction stimulus  203 . The stimulus  203  may be a pre-determined force and/or momentum. In embodiments in which the actuator  202  has a longitudinal axis, the force of the stimulus  203  may be applied along an axis parallel or angled with reference to the longitudinal axis of the actuator  202 , or along an arcuate path. In some embodiments, the actuator  202  may be coupled to a head-band configured to align or support the actuator  202  during the delivery of the bone conduction stimulus  203 . In some embodiments, the actuator  202  may be housed within a mechanically linked gantry that is hinge-ably mounted to a structure, such as a chair, a table, or the floor so that the generated stimulus can be delivered without the use of a handheld actuator device. 
     Some embodiments of the system  200  may be characterized as a rapid, computer-controlled and calibrated handheld device that can deliver a plurality of bone conduction stimuli  203 . Several applications of the system  200  have been contemplated. It is noted that the described applications are merely illustrative and other applications relating to clinical screening, testing, and diagnosis of the inner ear are applicable. Examples of applications for the systems disclosed herein include, but are not limited to, screening to monitor ototoxic drugs being administered in the hospital or in an ambulatory setting (e.g., a chemotherapy unit), screening for patients being admitted to the hospital to determine abnormalities of either gravitational receptor and also between inner ears (which may be useful as a predictor of hospital falls). A review of pathological conditions that have been studied using VEMPs, and to which the system  200  may be applied, is presented in K. D. Nguyen et al.,  Test - retest Reliability and Age - related Characteristics of the Ocular and Cervical Vestibular Evoked Myogenic Potential Tests,  31(5) O TOL  N EUROTOL.  793-802 (2010); P. A. Wackym et al.,  Rapid cVEMP and oVEMP Responses Elicited by a Novel Head Striker and Recording Device,  33 O TOL  N EUROTOL.  1392-1400 (2012); and P. A. Wackym, Response to: Rapid cVEMP and oVEMP Responses Elicited by a Novel Head Striker and Recording Device. 34(4) O TOL  N EUROTOL.  779-780 (2013). 
     Furthermore, it is recognized that evaluations of the temporal aspects of gravitational receptor responses (e.g., the latency between the stimuli and the measured signal) may be used as a precursor to diagnose some types of inner ear vestibular disorders. For example, it is observed that with some patients with some types of inner ear vestibular disorders, the wave morphology of an action potential, present when a disease is active, deteriorates and returns to normal after surgical intervention. Similar disruptions in wave morphology can be seen with auditory brainstem evoked responses with certain auditory disorders. However, conventional stimulus techniques have made such morphologies challenging to detect. Various embodiments of the systems disclosed herein may enable the detection of altered wave morphology for the bone conduction stimulus-based physiological response monitoring in a manner that is more detectable than achievable with acoustic stimuli. As noted above, the altered wave morphology may be a marker of an inner ear disease, and may be detected more readily with various embodiments of the systems disclosed herein than conventional technologies. Similarly, it is also observed that a shorter latency of the cVEMP response may be present in superior canal dehiscence patients pre-operation and that the latency may return to normal after a surgical correction. cVEMP and oVEMP responses have been reported to change when recorded pre- and post-operations. Consequently, various embodiments of the systems disclosed herein may enable the detection of the shorter latency of the cVEMP response, and thus detection of superior canal dehiscence. More generally, various embodiments of the systems disclosed herein may enable the detection of otic capsule dehiscence syndrome, which may include superior, lateral, posterior semicircular canal dehiscence, perilymph fistula and otic capsule dehiscence that cannot be seen with current imaging techniques. Otis capsule dehiscence syndrome may create a third window in the inner ear, resulting in an increased amplitude of response and a decreased stimulation threshold detectable using various ones of the embodiments disclosed herein. Various embodiments disclosed herein may be useful in detecting endolymphatic hydrops, a fluid build up of the central compartment of the inner ear that occurs with many disorders, including otic capsule dehiscence syndrome. In addition, various embodiments of the systems disclosed herein may have application in any audiology, otology/neurotology, and neurology, or otolaryngology practice as a diagnostic tool. 
     Various embodiments disclosed herein may usefully detect gravitational receptor asymmetries. In particular, the cVEMP, oVEMP and oculometric measurement techniques disclosed herein may be used to determine a strength or magnitude of a patient&#39;s response on each side. The two sides may then be compared and asymmetries identified. Various embodiments disclosed herein may usefully identify patients who are at risk of hospital falls by determining weakness or absence of gravitational receptor function (e.g., by measuring and determining a degree of gravitational receptor function weakness or loss). 
       FIG. 3  illustrates an example of an electrically driven actuator  202 , according to various embodiments. The electrically driven actuator  202  may include an actuation element  302  that is coupled to an impactor  304 , for example, via a shaft  305 . In some embodiments, the actuation element  302  may be rigidly coupled to the impactor  304 . The actuation element  302  may be provided in a housing  314 . 
     In use, the impactor  304  may transmit a force to a skull bone  306  of a patient  201  by impacting the skull of the patient  201 . In some embodiments, the impactor  304  may be cushioned or malleable, and may act as a “hammer.” An end of the impactor  304  that is closest to the skull during use may be formed as, for example, a pad. The impactor  304  may include a cushion material, such as a suitable polymer material or felt. 
     The actuation element  302  is configured to accelerate the impactor  304  in a direction  307  from a start location  308  to a striking location  310  so as to deliver a pre-defined force or momentum  312 . The pre-defined force or momentum  312  may be of sufficient magnitude to saturate a gravitational receptor in the skull of the patient  201 . For example, in some embodiments, a pre-defined force  312  may have a magnitude between 1 and 500 Newtons (N). The actuation element  302  may be adapted to operate in a near silent manner (e.g., less than 50 dB HL) when accelerating the impactor  304 . In an embodiment, the actuation element  302  may be a voice-coil linear actuator. An example of a voice-coil linear actuator that may be included in the actuation element  302  in some embodiments is the Model No. NCC14-15-023-1PBS non-communication DC voice-coil linear actuator manufactured by H2W Technologies, Inc. (Santa Clara, Calif.). A voice-coil linear actuator may include a permanent magnet and a voice-coil that are adapted to move in relation to one another when the coil is powered. The magnet and voice-coil may be situated in a bearing system. In some embodiments, the actuation element  302  may include multiple voice-coil linear actuators operating as an array to increase the peak force that may be delivered. A voice-coil mechanism utilizes the relationship between electrical and magnetic fields to induce an axial force proportional to the driving current, and may have advantageously low friction force and high frequency loading that cannot be delivered by conventional pneumatic bone conduction systems. Minimizing bearing friction and maintaining a substantially linear voltage-to-force relationship during the entire stroke length may improve performance. 
     The striking location  310  (also referred to as a “striking point”) refers to a position of the impactor  304  when the impactor  304  impacts the head. The start location  308  (also referred to as a “starting point”) generally refers to a position of the impactor  304  prior to undergoing actuation by the actuation element  302 . The striking location  310  may be located between the start location  308  and the location of maximum extension of the impactor  304  (i.e., the point along the path of travel of the impactor farthest away from the start location  308  in a direction toward the striking location  310 ). In some embodiments, the actuation element  302  may be adapted to decelerate  311  the impactor  304  as the impactor  304  approaches the striking location  310  to lessen the sound generated by the impact. 
       FIGS. 4A-4G  illustrate various aspects of an example actuation element  302 , according to various embodiments. 
     The actuation element  302  may include an energy storage element to store potential energy to be release during the delivery of the stimulus. The energy storage element may be, for example, an electrical energy storage element (e.g., a capacitor) or a mechanical storage element (e.g., one or more springs).  FIG. 4A  illustrates an example actuation element  302  adapted to accelerate the impactor  304  (not shown) in a direction  350 , according to various embodiments. The actuation element  302  of  FIG. 4A  includes an electrically-actuated assembly  402  (such as a solenoid or a voice-coil) and a spring assembly  404  arranged to accelerate a mass  406 . The spring assembly  404  includes at least one spring (or a series thereof) that may be mounted to the housing  314 . The mass  406  may be coupled to the impactor  304  such that an acceleration of the mass  406  results in an acceleration of the impactor  304 . For example, the mass  406  may be rigidly coupled to the impactor  304  via the shaft  305 . The actuation element  302  may have a travel length (measured between its point of travel farthest from the striking location  310  and its point of travel closest to the striking location  310 ) over which the actuation element  302  may travel so as to provide the mass  406  (and other bodies coupled thereto) with a pre-defined momentum (e.g., having a pre-defined velocity) at the time of stimulus delivery. To accelerate the mass  406 , the electrically actuated assembly  402  may be energized with an electric potential having a first polarity to cause the mass  406  to move in a negative direction  408  (i.e., away from the striking location  310 ) to load the spring assembly  404  (e.g., put the one or more springs included in the spring assembly  404  into compression). Subsequently, the electrically actuated assembly  402  may be energized with an electric potential having a second polarity (opposite of the first polarity) to cause the mass  406  to move in a positive direction  410  (i.e., toward the striking location  310 ) to unload the spring assembly  404 . In unloading, the spring assembly  404  augments the force in the direction  410  provided by the electrically actuated assembly  402  as a result of the application of the electric potential of the second polarity. The resulting force may be expressed as shown below in Equation 1, in which F total  is the total force exerted on the mass  406 , F electrically-actuated assembly  is a force resulting from the electrical energy applied to the electrically-actuated assembly  402 , and F spring  is a force resulting from the unloading of the spring assembly  404 .
 
 F   total   =F   electrically-actuated assembly   +F   spring   (1)
 
     F spring  may be expressed as ½kx 2  where k is a spring constant of the spring assembly  404 , and x is a displacement in the negative direction  408 , as understood in the art. 
     Alternatively, the actuation element  302  may be adapted with a spring assembly  404  that is loaded by being put in tension. An example of such an embodiment is illustrated in  FIG. 4B . 
     To provide the electric potential of the first or second polarity, the electrically actuated assembly  402  may receive a waveform of varying voltage and current from the controller  204  (not shown). For example, the waveform may be sinusoidal, triangular, stepped, skewed, or complex (e.g., a wavelet).  FIG. 4C  illustrates examples of various types of waveforms applied to the electrically-actuated assembly  402 . Sub-figures ( 1 ) to ( 5 ) show various waveforms, including a sinusoidal, triangular, stepped, skewed, and square waveform. Portions of the waveforms on one side of the x-axis may have a first polarity and portions of the waveforms on the other side of the x-axis may have a second polarity. In particular, each waveform may include a first electric potential  414  having a first polarity and a second electric potential  416  having a second polarity, which is opposite of the first polarity. The peak voltage or current applied at the first and second polarity may also differ, examples of which are illustrated in sub-figures ( 6 ) and ( 7 ) of  FIG. 4C . Differing peak voltages or currents may be employed to vary the magnitude of the bone conduction stimulus. The peak voltages or currents may be adjustable by an operator of the systems disclosed herein to adjust the magnitude (e.g., peak force or momentum) of the impact between the impactor  304  and the patient  201 , thus providing a scalable impact. The differing peaks, shapes, averages, etc., may provide flexibility in the measurement or testing, and may allow practitioners to select the parameters of the measurement to perform different types of tests that may be suitable for different types of patients and/or conditions. For example, an operator may scale the impact in accordance with a patient&#39;s comfort level, or in accordance with other clinical guidelines. In some embodiments, the waveforms provided to the electrically actuated assembly  402  may be analog waveforms. In some embodiments, the waveforms generated by the controller  204  and provided to the electrically actuated assembly  402  may be generated by the controller  204  in a digital form, then converted to an analog form using a suitable analog to digital (ND) converter. 
     In some embodiments, the electrically-actuated assembly  402  may receive a waveform of varying voltage and current from the controller  204  to assist both in positively accelerating the mass  406  toward the striking location  310  and in controllably decelerating the mass  406  prior to impact. For example, the waveform may include a portion having a third electric potential, subsequent to a portion having the second electric potential, having the first polarity. An example of this is illustrated in  FIG. 4C  subfigure ( 8 ), in which a first square wave portion (e.g., the first electric potential  414 ) having a first polarity is followed by a second square wave portion (e.g., the second electrici potential  416 ) having a second polarity, and in which the second square wave portion  416  is followed by a third square wave portion  412  having the first polarity. 
     Referring back to  FIG. 3 , the electrically driven actuator  202  may include a housing  314  in which the actuation element  302  may be disposed. The impactor  304  may be disposed within or external to the housing  314 . 
     The housing  314  may include a guide  316  to maintain the orientation and alignment of the impactor  304  in relation to the actuation element  302 . In some embodiments, the guide  316  may be a linear guide, which may be oriented parallel to or angled with reference to a longitudinal axis of the electrically driven actuator  202 .  FIGS. 4A and 4B , for example, show the guide  316 , which may take the form of a bushing, sleeve bearing, journal bearing, or other suitable guide mechanism. In some embodiments, the guide  316  may take the form of a shaft that rotates around a hinge. For example,  FIG. 4D  depicts an embodiment in which the impactor  304  is coupled with a shaft  418  that rotates around a hinge  420  until the impactor  304  contacts the patient  201 . In another embodiment, the guide  316  may allow for angular movements around a rotational axis. For example,  FIG. 4E  depicts an embodiment in which the guide  316  is as an axle holding a mass  406  in a socket  424 . The impactor  304  may be coupled with a face of the mass  406  (e.g., as shown in  FIG. 4E ). 
     The electrically driven actuator  302  may include a deceleration element adapted to controllably decelerate the mass  406  prior to the impact of the impactor  304  and the patient  201 , thereby allowing for near-silent operation.  FIGS. 4F and 4G  each illustrate a portion of embodiments of an electrically driven actuator  302  including one or more deceleration elements. The deceleration elements may operate in conjunction with the decelerating function of the electrically-actuated assembly  402 , discussed above. As shown in  FIGS. 4F and 4G , the deceleration element may include a spring  426  (or a series thereof) adapted to remove energy from the impactor  304  and store it (e.g., in compression or tension) as the impactor  304  approaches the striking location  310 . As also illustrated in  FIGS. 4F and 4G , the deceleration element may include cushioning elements  428 , such as an elastic or deformable stopper, adapted to insulate any moving components from non-moving components. For example, as shown in the example of  FIG. 4F , the cushioning elements  428  may be situated to insulate the mass  406  from directly contacting a portion of the housing  314  or static components affixed thereto. As another example, as shown in the example of  FIG. 4G , the cushioning elements  428  may be situated to insulate moving components within the electrically actuated assembly  402 . In the embodiment of  FIG. 4G , a cushioning element  428  may take the form of a stopper situated between a stationary component  430  and a non-stationary component  432  of the electrically actuated assembly  402 ). The deceleration element  318  may take any of these forms, and may aid in the controllable deceleration of the mass  406 . 
     In some embodiments, the electrically driven actuators  202  disclosed herein may take the form of a handheld actuator.  FIGS. 5A and 5B  illustrate the electrically driven actuator  202  instantiated as a handheld actuator  500 , according to various embodiments.  FIG. 5A  illustrates a disassembled view of the handheld actuator  500 , and  FIG. 5B  illustrates a cut-out view of the handheld actuator  500  when assembled. As shown in the disassembled-view of  FIG. 5A , the handheld actuator  500  includes a housing  314  that predominantly forms a body of the handheld actuator  500 . A voice-coil linear actuator assembly  501  is provided as the actuation element  302 . The voice-coil linear actuator assembly  501  may include a permanent magnet  502 , a voice-coil  504 , a polymer stopper  506 , an impact spring  508 , bushings  510 , and a shaft  512 . The handheld actuator  500  may also include an impact pad  514  (as the impactor  304 ) and contact force spring  516 . 
     When assembled, and at rest (e.g., not energized), the voice-coil linear actuator assembly  501  may be secured substantially within to the housing  314 . A locking screw (not shown) or other mechanism may be employed to retain the voice-coil linear actuator assembly  501  in relation to the housing  314 . The voice-coil  504  and shaft  512  may be tapered against one another. The voice-coil  504  may be disposed in the permanent magnet  502  with the impact spring  508  and the polymer stopper  506  disposed therebetween. The voice-coil  504  may be arranged so as to be moveable relative to the permanent magnet  502 . The permanent magnet  502  may have an inner bore that may be longitudinally aligned with the bushings  510 . The shaft  512  may be disposed in the bushings  510  and may extend beyond the permanent magnet  502  to substantially permanently connect to the impact pad  514 . The shaft  512  may have an elongated region and an end region  518 . The end region  518  may be disposed against the contact force spring  516  that is situated between the voice-coil linear actuator assembly  501  and the housing  314 . The housing  314  may include a cabling assembly  520  that allows for cabling (not shown) to connect the voice-coil  504  and the controller  204  (not shown). The cabling may include power and ground signal pathways. Other signal pathways may be included in the cabling to allow for communication of sensors and data signals from sensors (not shown) and on-board electronics (such as a trigger switch, not shown) situated in the handheld actuator  500 . In some embodiments, some of the data transmitted between the handheld actuator  500  and the controller  204  or other components may be transmitted wirelessly using appropriate hardware included in the transmitting and receiving devices (e.g., Bluetooth hardware). In some embodiments, the handheld actuator  500  (or any of the actuators disclosed herein) may be battery powered. 
     During operation (e.g., the delivery of a bone conduction stimulus), the handheld actuator  500  may be positioned so that the impact pad  514  is proximate to the skull of the patient  201 . In particular, the handheld actuator  500  may be positioned so that the striking location  310  is proximate to the desired impact point on the skull of the patient  201  (i.e., start location  308 ). The impact pad  514  may be positioned against the scalp of the patient  201  with a predetermined loading force, prior to application of an impact. In some embodiments, the predetermined loading force may be approximately 1.5 kilograms. 
     Power may be applied (for example, from the controller  204 ) at a first voltage polarity (e.g., positive) through the cabling to the voice-coil  504 . The voice-coil  504  may generate a repulsive force with the permanent magnet  502  due to the power applied at the first voltage polarity, causing the voice-coil  504  to move in the loading direction  522 , away from the striking location  310 . In doing so, the voice-coil  504  may push the end region  518  of the shaft  512  (disposed against the voice-coil  504 ) to also move in the loading direction  522 , thereby causing the contact force spring  516  to compress. The voice-coil  504  and permanent magnet  502  may be considered as the electrically actuated assembly  402  (as shown in  FIGS. 4A and 4B ) configured to accelerate the mass  406  (e.g., the voice-coil  504  and the shaft  512 ) while loading the spring assembly  404  (e.g., the contact force spring  516 ). The power applied at the first voltage polarity may be considered the first electric potential  414  (e.g., as shown in  FIG. 4C ). Actuator power may be limited to a safe and effective level by a hardware-coded limit setting on an amplifier, for example. In some embodiments, a software-coded power limit may also be included for redundancy. 
     After applying power at the first voltage polarity, a voltage of opposite polarity may be applied to the voice-coil  504 . The power applied at the second voltage polarity may be considered the second electric potential  416  (e.g., as shown in  FIG. 4C ). In response, the voice-coil  504  may generate an attractive force with the permanent magnet  502 , causing the voice-coil  504  to move in the impact direction  524  toward the striking location  310 . With the repulsive force removed, the contact force spring  516  may stretch from its compressed state, thereby assisting or augmenting the force provided by the attractive force generated by the permanent magnet  502  and the voice-coil  504  in response to the power applied at the second voltage polarity. The resulting force may be characterized as discussed above with reference to Equation 1. 
     As the shaft  512  moves in the impact direction  524 , the impact pad  514  may move toward the striking location  310 . As the impact pad  514  approaches the striking location  310 , the voice-coil  504  may begin to compresses the impact spring  508 . The impact spring  508  may thus act as the deceleration spring  426  as shown in  FIGS. 4F and 4G , and may controllably decelerate the mass  406  (e.g., the voice-coil  504  and the shaft  512 ). This controlled deceleration may prevent acoustic noise generated by a high-speed collision of two components of the handheld actuator  500 , thereby allowing for near-silent operation of the handheld actuator  500  relative to conventional actuators. The polymer stopper  506  may be situated between the voice-coil  504  and the permanent magnet  502  and may act as a cushioning element  428  (e.g., as shown in  FIGS. 4F and 4G ), assisting in the controlled deceleration of the mass  406  (e.g., the voice-coil  504  and the shaft  512 ). The deceleration time may be short in comparison to the acceleration time, thereby having minimal effects on the impact energy. Audible impact noise may also occur during rebound. The mass  406  (e.g., the voice-coil  504  and the shaft  512 ) may be arranged to push against the contact force spring  516 , which may act to prevent a rebound impact. 
     It should be appreciated by those skilled in the art that, in some embodiments, the voice-coil  504  and the permanent magnet  502  may operate to produce an attractive force therebetween to load the contact force spring  516  and then to produce a repulsive force therebetween to accelerate the impact pad  514  toward the striking point  310 . It should also be appreciated by those skilled in the art that a voice-coil actuator having a static voice-coil and a moving permanent magnet may be employed rather than a static permanent magnet and moving voice-coil (as illustratively shown in  FIGS. 5A and 5B ). 
     The voice-coil  504  and shaft  512  may be considered to be suspended between two opposing springs (i.e., the contact force spring  516  and the impact spring  508 ). This suspension contributes to the silent or near-silent operation of the handheld actuator  500  by allowing for smooth and rapid transitions between each of the bone conduction stimuli. The polymer stopper  506  may provide further cushioning between moving components, though the components may be situated apart such that they do not contact each other between each delivery of a bone conduction stimulus. The impact pad  514  may be configured to contribute to the silent or near-silent operation of the handheld actuator  500 . For example, in some embodiments, the impact pad  514  may include a wide surface area for impact (up to or greater than the cross-sectional area of the housing  314  of the handheld actuator  500 ). As such, energy from the handheld actuator  500  may be evenly distributed to the skull bone. Cushioning included on the impact pad  514  may also reduce acoustic noise. 
     As discussed herein, some embodiments of the handheld actuator  500  may enable delivery of bone conduction stimuli that are functionally silent, variable in force and impact, and purposely formed as modulated pulses. As such, the bone conduction stimuli may be synchronized with sensor measurements (e.g., action potential recordings or captured images) allowing for integrated data analysis, such as analysis to extract latency information between responses and other features of the measured response. It is observed that some embodiments of the handheld actuator  500  may operate at 4-10 hertz (Hz), which may be significantly faster than conventional solenoid-based cone conductions systems. As such, the handheld actuator  500  may enable more deliveries of the bone conduction stimuli in a given time period, allowing for a shorter testing protocol as well as opportunities for processing of the measured signal (e.g., averaging) to improve the signal-to-noise ratio of the measurement. For example, in some embodiments, testing using the handheld actuator  500  may be completed in ten minutes or less, a significant reduction relative to conventional approaches which may take thirty minutes or more. The shorter testing protocol may also make it easier for an operator holding the handheld actuator  500  to maintain the position of the handheld actuator  500  over the striking position on the patient&#39;s skull without drifting. 
     In alternate embodiments, either one of the two opposing springs (the contact force spring  516  and the impact spring  508 ) may be “pre-loaded” (i.e., under compressive or repulsive load when the handheld actuator  500  is de-energized). The pre-loading may be employed to bias the spring to increase or decrease the peak impact force that may be delivered by the handheld actuator  500 . For example, the voice-coil linear actuator assembly  501  may be adapted to move in relation to the housing  314  to pre-load the contact force spring  516  at pre-defined increments along the housing  314 . In some embodiments, the pre-load may also retain the mass  406  at the pre-defined start location  308  during rest. As such, when the voice-coil linear actuator assembly  501  is energized to load the contact force spring  516 , a greater force may be released when the contact force spring  516  is unloaded. 
     Other embodiments may deliver a bone conduction stimulus in a silent or near-silent manner.  FIGS. 6A and 6B  illustrate an electrically driven actuator  202  in two different positions, according to various embodiments. Rather than being rigidly coupled together (e.g., as discussed above with reference to the embodiments of  FIGS. 5A and 5B ), the impactor  304  may be movably coupled to the actuation element  302 . The actuation element  302  may still be adapted to accelerate the impactor  304  from the start location  308  to the striking location  310  to deliver a pre-defined force or momentum. However, the actuation element  302  may accelerate an intermediate component  602  (e.g., a ram) that may transfer the kinetic energy of the actuation element  302  to the impactor  304 . For example,  FIG. 6A  depicts the intermediate component  602  in a “retracted” position, and  FIG. 6B  depicts the intermediate component  602  in an “extended” position by which the intermediate component  602  may contact the impactor  304  and transfer the kinetic energy of the actuation component  302  to the impactor  304 . As such, the impactor  304  may be modeled as an independent moving system relative to the actuation element  302 . 
     As a result of the controllability of the handheld actuator  500  to deliver bone conduction stimuli that are variable in force and purposely formed as modulated pulses (e.g., by allowing the operator to select waveforms and amplitudes via the interface unit  210 ), the handheld actuator  500  may enable automated sequences of stimuli having varying waveform shapes, timing, and/or magnitudes for use in measurement and testing.  FIGS. 7A-7D  illustrate example testing sequences that may be used for measuring gravitation receptor functions, according to various embodiments. 
     In some embodiments, a testing sequence may include stimuli of uniform peak magnitude, shape and duration. For example,  FIG. 7A  illustrates a plot (having an x-axis  724  representing time and a y-axis  726  representing delivered force) of a testing sequence  700  of different stimuli (referred to as “test signals”)  702  with uniform peaks, shape, and duration. Each test signal  702  may be the product of a power waveform (e.g., the waveforms depicted in  FIG. 3C ). 
     In some embodiments, the testing sequence may be a sequence of gradually varying stimuli (e.g., stimuli of increasing or decreasing amplitude and duration), such as a ramp. For example,  FIG. 7B  illustrates a plot (having an x-axis  724  representing time and a y-axis  726  representing delivered force) of a testing sequence  704  of test signals having gradually decreasing amplitude. For example, a second test signal  706  follows a first test signal  708  and has a lower peak or average amplitude. Similarly, subsequent test signals may have gradually increasing or decreasing amplitudes. For example, the peak, average, or other representative statistic of each test signal may differ by at least 20% between each consecutive test signal. Of course, other variations may be used. In one embodiment, the sequence  700  may include a fixed number n of test signals. In another embodiment, the test sequence  700  may be adaptive, in which test signals of decreasing amplitude are applied until no measured response (e.g., cVEMP, oVEMP, and/or oculometric) is observed. The test sequence  700  may include a last test signal  710 , which may be a supramaximal stimulus (i.e., being of strength significantly above that required to activate all the nerve or muscle fibers in contact with one or more of the electrodes (e.g., included in the plurality of sensors  206 ) or to be detectable in captured images of the eye). In some embodiments, a testing sequence may include a sequence of test signals of gradually increasing intensity (e.g., as quantified by the test signals&#39; peak, or average) to determine the strength of the supramaximal stimulus. 
     As shown in  FIGS. 7A and 7B , the test sequence may form a continuous waveform. Alternatively, the test sequence may include pre-defined durations  712  between each of the test signals, as shown in  FIGS. 7C and 7D . The pre-defined durations  712  may be consistent between the test signals in a test sequence, as shown for the durations  712   a  in  FIG. 7C . The pre-defined durations  712  may vary between each test signal, as shown in  FIG. 7D  (as durations  712   b ,  712   c ,  712   d , and  712   e ). 
       FIGS. 7E-7G  illustratively show hypothetical outputs of a test of a patient&#39;s gravitational receptors in response to applying the testing sequence of  FIGS. 7A-7D . Specifically,  FIG. 7E  illustrates a display  714  of one or more action potential signals measured from the sensors  206  (e.g., in response to the pattern of  FIG. 7A ) in an embodiment in which the sensors  206  include electrodes. In some embodiments, the display  714  may include a representation of cVEMP  714   a , oVEMP  714   b , or both. The display  714  may indicate various characteristics of the test stimuli applied, such as (a) the peak force and/or momentum applied  716 , (b) the number of stimuli applied  730 , (c) the type of test sequence (e.g., ramp, adaptive, etc., not shown). The display  714  may indicate a time of initiation of delivery  732  and a time  718  (referred to as a latency time) between the initiation time  732  and an observed peaked measured response. For example, the oVEMP n10 potential may be identified as the first distinctive and replicated peak in the oVEMP waveform  714   b , post-stimulus, and may typically occur around 8-12 milliseconds post-stimulus. The oVEMP p16 potential may be identified as the first distinctive and replicated trough in the oVEMP waveform  714   b  following the peak n10, and may typically occur around 16 milliseconds post-stimulus. The cVEMP p13 potential may be identified as the first distinctive and replicated trough in the cVEMP waveform  714   a , post-stimulus, and may typically occur around 10-14 milliseconds post-stimulus. The cVEMP n23 potential may be identified as the first distinctive and replicated peak in the cVEMP waveform  714   a , post-stimulus, and may typically occur around 19-23 milliseconds post-stimulus. The displayed signals may be an average of the signals (e.g., a windowed average). The display  714  may include statistical information, such as distribution, maximum range of amplitude and/or latency (e.g., normalized to stimulus intensity), minimum range of amplitude and/or latency (e.g., normalized to stimulus intensity), etc. 
     The oVEMP waveform  714   b  may include a left side oVEMP waveform  750  and a right side oVEMP waveform  75 . The cVEMP waveform  714   a  may include a left side cVEMP waveform  754  and a right side cVEMP waveform  756 . As shown, the system  200  may record the time of the initial strike and the time to the initial peak and then calculates the time difference; in the example of  FIG. 7E , these time differences are 9.5 milliseconds (right side oVEMP waveform  752 ), 9.9 milliseconds (left side oVEMP waveform  750 ), 13.2 milliseconds (left side cVEMP waveform  754 ) and 13.7 milliseconds (right side cVEMP waveform  756 ). 
       FIGS. 7F and 7G  illustrate hypothetical displays  720  and  722 , respectively, of an input-output test, according to various embodiments. Impact patterns in which the stimuli varies (e.g., the patterns illustrated in  FIGS. 7B-7D ) may be used to perform an input-output test.  FIG. 7F  shows the amplitude (e.g., characterized by peaked magnitude, averaged magnitude, etc.) of a cVEMP measured signal  724  and oVEMP measured signal  726  on the y-axis, plotted against the stimuli (e.g., characterized by peak force, average force, peak momentum, average momentum, etc.) on the x-axis  728  (shown as “F1” to “Fn”). For example, the system  200  may acquire eight measured signals in response to 1 second of impacts delivered at 8 Hz at a given force, and may perform a set of such measurements at each of ten different forces for a total of ten seconds of testing and/or measurement. Each measurement for each given force may be averaged with the peak or average information being displayed.  FIG. 7G  shows the latency (e.g., the time  718  illustrated in  FIG. 7E ) of a cVEMP measured signal  730  and an oVEMP measured signal  732  on the y-axis, plotted against the stimuli (e.g., characterized by peak force, average force, peak momentum, average momentum, etc.) on the x-axis  728 . Of course, various numbers of sets and numbers of measured signal per set may be employed. Clinicians may review these plots to identify unique patterns associated with Meniere&#39;s disease, the genetic loss of gravity receptor function, the development of ototoxicity during antibiotic or chemotherapy administration, superior canal dehiscence, or other conditions. 
     In some embodiments, the system  200  may be configured for novel measurement schemes and data analysis. For example, in some embodiments, the system  200  may compute and display an input-output comparison of the the gravitational receptor functions (e.g., as represented by measured action potential(s) or the analysis of captured images of the eye). An input-output comparison may be based on two or more impact patterns, each having different amplitude and/or frequency. The input-output comparison may analyze the difference between the patient responses to the two impact patterns, and present the difference in response as a function of the difference in impact pattern. The focus in some such comparisons may be on the relative differences in the amplitude or other characteristics of the two responses, rather than the absolute amplitudes or other characteristics of the responses. Such comparisons have not been previously studied, and may yield valuable clinical data. 
     In another example, the system  200  may compute and display normalized patient responses to various impact patterns (e.g., normalized to the average or maximum magnitude of the forces of the impacts in the impact pattern). The normalized response may be employed in a clinical or research protocol to determine subtle defects of the gravitational receptors and differences thereof. 
     In another aspect of some of the embodiments disclosed herein, various methods and apparatus may provide for consistent and quickly deployable measuring of the oVEMP. An apparatus may be adapted to be quickly and easily seated (like a mask) over at least a portion of a patient&#39;s face. One or more electrodes may extend from the apparatus and may be situated over at least a portion of the extraocular muscle of at least one eye, including the inferior oblique muscle. The apparatus and electrode may not impinge on the globe of the eye or the extraocular muscle, nor limit motions of the globe, thus providing for a clearer and more robust measurement of the oVEMP response. Commercial swim goggles may result in globe entrapment, and thus may be functionally useless for measurement purposes. 
       FIG. 8  illustrates a mask  209  for measuring oVEMP response, according to various embodiments. As used herein, a “mask” refers to any eyewear that, in use, seats over a portion of a face of a person without applying substantial pressure to the globes of the eyes and the extraocular muscles. A mask may be a cover, a protecting goggle, glasses, etc. Various ones of the mask embodiments disclosed herein may enable testing to be performed at a patient&#39;s bedside, rather than requiring the patient to travel to a designated testing location. 
     The mask  209  may include a frame  802  and is configured to seat over a portion of the face of the patient  201 . For example, the frame  802  may rest on the ears  804  and nose  806  of the patient  201 . In an alternate embodiment, the frame  802  may rest on the cheeks  808 . In yet another embodiment, the frame  802  may suspend or extend from a band (not shown) wrapped fully or partially around the head. 
     The mask  209  may include at least one sensor  206  adapted to seat over a portion of at least one of the extraocular muscles when the mask  209  is positioned on the head of the patient  201 . The sensor  206  may be a surface electrode, such as a preamplified electrode. In some embodiments, the sensor  206  may extend from the frame  802  via a bridge  810  to rigidly connect with the frame  802 . In another embodiment, the bridge  810  may be an articulable arm that may extend, pivot, flex, and/or rotate to allow the sensor  206  to be adjusted in relation to the face of the patient  201 . An example of an articulable arm that may be suitable for some embodiments is the Model No. 96130 arm manufactured by Moffatt Products, Inc. (Watertown, S. Dak.). Use of a preamplified surface electrode as the sensor  206  may enable detection of an evoked response resulting from reduced stimuli intensity relative to passive surface electrodes. The frame  802  may have a perimeter portion  812  disposed in front of the eyes when in use, and may surround glass or plastic lenses or may not include lenses. 
     In some embodiments, the mask  209  of  FIG. 8  may include one or more other sensors, such as accelerometers. These other sensors may be included in the frame  802 , in an elastic band, or may be coupled with the mask  209  via one or more wires. These other sensors may provide data useful for normalization and/or feedback, as discussed above. 
       FIG. 9  illustrates another embodiment of a mask  209  for measuring oVEMP response. The mask  209  may include a frame  802  to seat over the nose of the patient. The frame  802  may be connected to a stretchable band  902  adapted to wrap around the head of the patient  201 . 
     As discussed above, some methods and apparatus may provide for consistent and quickly deployable measuring of a patient&#39;s physiological response (e.g., the cVEMP, the oVEMP, and/or the oculometric response). To provide for such measurements, some embodiments of an apparatus may provide a resting area for the patient&#39;s chin while causing the patient to lean (i.e., tilt or bend) forward. In doing so, the apparatus may cause the patient to flex his or her neck in a manner that causes at least a portion of the sternocleidomastoid muscles to contract without straining the temporomandibular joint and/or neck and spine. 
       FIGS. 10A-10C  illustrate several views of an apparatus  1000  for measuring physiological responses, according to various embodiments. Specifically,  FIG. 10A  shows a perspective view,  FIG. 10B  shows a front view, and  FIG. 10C  shows a side view. The apparatus  1000  may be mounted on a table top  1002 . The table top  1002  may be motorized to be adjusted to a suitable height (along the z-direction) for the patient  201 . An example of a motorized table that may be suitable for some embodiments is Model No. 01-TBL001, manufactured by Woodlyn, Inc. (Arlington Heights, Ill.). The patient  201  may sit or stand proximal to the table top  1002 . The apparatus  1000  may include a chin rest  1004 , which may be adjustable in the z-direction. In some embodiments, the chin rest  1004  may be adjustable in other directions, including the x-direction and y-direction. The apparatus  1000  may include a handle  1006  as a hand rest. In some embodiments, the apparatus  1000  may be used with existing air-conduction VEMP systems or future to be developed VEMP delivery and recording systems. 
     The apparatus  1000  may be configured to allow for symmetric neck flexion of the patient  201  against the chin rest  1004 . The chin rest  1004  may include a pressure sensor  1008  to measure the pressure (e.g., the force) applied by the patient  201  to the chin rest  1004 . The measured pressure may be stored as part of the physiological response to normalize the physiological measured signal. The measured pressure may also be employed to normalize the physiological measured signal. The apparatus  1000  may include a laser guide to provide patterns on a surface or may include a bar with LED lights to which the patient  201  may draw his or her attention for the measurement and/or testing. Of course, other guide may be use, such as markings on the wall, etc. 
     The apparatus  1000  may include articulated arms  1010  to support sensors  206   a  (e.g., electrodes) placed over the sternocleidomastoid muscles for measuring cVEMP responses and/or sensors  206   b  (e.g., electrodes) placed over the inferior oblique muscles for measuring oVEMP responses. The articulated arm  1010  may take the form of any suitable one of the articulated arms described herein. The sensors  206   a  and  206   b  may include preamplified surface electromyogram (EMG) electrodes. In some embodiments, a soft band may be applied over sensors  206   a  to maintain the sensors over the sternocleidomastoid muscle. 
     The apparatus  1000  may include one or more arms  1040  to support one or more sensors  206   c  (e.g., video cameras) for measuring oculometric responses. The arms  1040  may take the form of any suitable one of the articulated arms described herein, or may be non-articulated. 
     In other embodiments, a mask  209  (e.g., the masks  209  of  FIGS. 8 and 9 ) may be outfitted with one or more video cameras to capture video of eye movement to characterize the oculometric response. These video cameras may be included in the mask  209  in addition to or instead of other sensors, such as electrodes and accelerometers. In some embodiments, a mask  209  that includes video cameras may be included in a conventional video oculography system. 
       FIG. 11  illustrates another embodiment of a mask  209  for measuring patient response, according to various embodiments. The mask  209  may include a frame  802  and is configured to seat over a portion of the face of the patient  201 . In particular, the frame may include a nose rest  1102  to rest on a nose of the patient  201 , and ear rests  1106  to rest on the ears of the patient  201 . 
     The mask  209  of  FIG. 11  may include at least one sensor  206  adapted to seat over a portion of at least one of the extraocular muscles when the mask  209  is positioned on the head of the patient  201 . As illustrated in  FIG. 11 , the mask  209  may include two sensors  206 . Each sensor  206  may be a surface electrode, such as a preamplified electrode, as discussed above. In some embodiments, the sensors  206  may be reusable; in other embodiments, the sensors  206  may be disposable, and may be swapped out and between patients. The sensor  206  may be coupled with the frame  802  via a bridge  810  (e.g., an articulable arm). The bridge  810  may include joints that allow the position of the sensor  206  to be adjusted in the medial to lateral direction (denoted by “A”), the superior to inferior direction (denoted by “B”), and the anterior to posterior direction (denoted by “C”) to accommodate the physical characteristics of the patient  201  and adjust the position of the sensors  206  in relation to the face of the patient  201 . In some embodiments, a disposable elastic wrap may be provided with the mask  209  to hold the electrodes over the sternocleidomastoid muscles. The disposable elastic wrap may be, for example, a self-adhering cohesive wrap as commonly used in bandaging applications. In some embodiments, the mask  209  of  FIG. 11  may include one or more other sensors, such as accelerometers. These other sensors may be included in the frame  802 , in an elastic band, or may be coupled with the mask  209  via one or more wires. These other sensors may provide data useful for normalization and/or feedback, as discussed above. 
       FIGS. 12A-12C  illustrate a graphical user interface for viewing patient responses, according to various embodiments. In particular,  FIG. 12A  depicts a first portion that may be arranged as the left column in a display,  FIG. 12B  depicts a second portion that may be arranged as the center column in a display, and  FIG. 12C  depicts a third portion that may be arranged as the right column in a display. The left column may include a display of the amplitude of each strike as a function of time. Drop-down menus below may allow the operator to customize the test parameters used. In particular, the drop-down menus may allow selection of the amplitude of the strike, number of strikes per second, elections regarding the way the data is recorded, analyzed, and displayed, and also the pattern of stimulus delivery. For example, the scaled delivery amplitude can be ascending, descending, or random over a fixed stimulus delivery interval. Alternatively it can be delivered with amplitude that is fixed. 
     The top four displays in the center and right columns plot the evoked potentials for the right and left cVEMP and oVEMP responses, respectively. The bottom displays in the center and right panel display the amplitude differential and latency differentials so that input-output functions can be measured. In some embodiments, the data may be captured and calculated for right and left cVEMP and oVEMP responses. The first column may include the display of the amplitude of each individual strike as a function of time. In some embodiments, only a subset of the portions of the graphical user interface illustrated in  FIGS. 12A-12C  may be included in a display together, and others may be accessible by selecting various on-screen options or may not be included at all. 
       FIGS. 13A-13C  illustrate a handheld electrically driven actuator  1300 , according to various embodiments. In particular,  FIG. 13A  is a perspective view of the handheld electrically driven actuator  1300 ,  FIG. 13B  is a cross-sectional view of the handheld electrically driven actuator  1300 , and  FIG. 13C  is an exploded view of the handheld electrically driven actuator  1300 . Some or all of the components of the handheld electrically driven actuator  1300  may be formed by 3D printing. As illustrated, Component  1  is the main handpiece, which may be rigidly secured to component  2 . This may allow the striking unit to be placed and secured inside of the handpiece during assembly. Note that a custom fabricated single spring may be placed so that when a 1.5 kg load is applied, component  2  is allowed to compress down onto component  4 , readying the device to be deployed. The actuator  1302  (e.g., a voice-coil motor) may be rigidly secured in place between components  3  and  5 . The striker shaft may impact component  4 , which may be rigidly secured to component  3 , thereby delivering the bone conduction stimuli to the patient&#39;s head when placed at, e.g., the Fz position. A spring  1304 , which may be custom manufactured, may create a uniform load before stimulus delivery when compressed. 
     The embodiments described above are intended to be merely exemplary; numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present disclosure as defined in any appended claims. 
     It should be recognized by one of ordinary skill in the art that the foregoing methodology may be performed in a video processing environment and the environment may include one or more processors for processing computer code representative of the foregoing described methodology. The computer code may be embodied on a non-transitory computer readable medium. For example, the computer code may be embodied in a computer program product. Additionally, the functions of the methods discussed herein may be distributed among a plurality of processors (either local or remote from one another). 
     The systems and methods disclosed herein may be embodied in many different forms, including, but in no way limited to, computer program logic for use with a processor (e.g., a microprocessor, microcontroller, digital signal processor, or general purpose computer), programmable logic for use with a programmable logic device (e.g., a Field Programmable Gate Array (FPGA) or other programmable logic device (PLD)), discrete components, integrated circuitry (e.g., an Application Specific Integrated Circuit (ASIC)), or any other means including any combination thereof. As used herein, the term “logic” may refer to a programmed computing device or circuitry. 
     Computer program logic implementing all or part of the functionality previously described herein may be embodied in various forms, including, but in no way limited to, a source code form, a computer executable form, and various intermediate forms (e.g., forms generated by an assembler, compiler, networker, or locator). Source code may include a series of computer program instructions implemented in any of various programming languages (e.g., an object code, an assembly language, or a high-level language such as Fortran, C, C++, JAVA, or HTML) for use with various operating systems or operating environments. The source code may define and use various data structures and communication messages. The source code may be in a computer executable form (e.g., via an interpreter), or the source code may be converted (e.g., via a translator, assembler, or compiler) into a computer executable form. 
     The computer program may be fixed in any form (e.g., source code form, computer executable form, or an intermediate form) either permanently or transitorily in a tangible storage medium, such as a semiconductor memory device (e.g., a RAM, ROM, PROM, EEPROM, or Flash-Programmable RAM), a magnetic memory device (e.g., a diskette or fixed disk), an optical memory device (e.g., a CD-ROM), a PC card (e.g., PCMCIA card), or other memory device. The computer program may be fixed in any form in a signal that is transmittable to a computer using any of various communication technologies, including, but in no way limited to, analog technologies, digital technologies, optical technologies, wireless technologies, networking technologies, and internetworking technologies. The computer program may be distributed in any form as a removable storage medium with accompanying printed or electronic documentation (e.g., shrink wrapped software or a magnetic tape), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the communication system (e.g., the Internet or World Wide Web). 
     Hardware logic (including programmable logic for use with a programmable logic device) implementing all or part of the functionality previously described herein may be designed using traditional manual methods, or may be designed, captured, simulated, or documented electronically using various tools, such as Computer Aided Design (CAD), a hardware description language (e.g., VHDL or AHDL), or a PLD programming language (e.g., PALASM, ABEL, or CUPL). 
     Wireless communication may include a transmission of information as a signal over any portion of the electromagnetic spectrum, including infrared, and radio. The transmission of the information may be part of a wireless network having a defined set of protocol (i.e., IEEE 802.11, Zigbee, WPAN, and Bluetooth). 
     Various embodiments of the bone conduction systems and techniques disclosed herein may provide a substantial societal benefit by one or more of: lower production costs creating greater opportunity for these systems to be purchased and used by more hospitals, clinics, and clinicians&#39; offices; reducing the test time, allowing more efficient screening for ototoxicity and hospital fall risk as well as allowing the testing of groups that currently cannot tolerate testing such as children, the elderly, and those with conductive hearing loss; more accurate assessment of post-military injury of the inner ear; and more accurate diagnosis of inner ear disorders that produce gravitational receptor dysfunction. 
     Some embodiments may allow the precision control of bone conduction stimuli necessary to test novel stimulus paradigms, determine the specific evoked potential threshold, determine the maximal utricular or saccular response, and to be able to calculate input-output functions. By contrast, commercially available air-conduction VEMP systems can only determine the event threshold, and because these systems do not have FDA clearance or approval, the manufacturers instruct clinicians not to use their devices for performing VEMP studies clinically. 
     Additionally, existing video oculography systems are designed to measure eye movements when a patient&#39;s rotational receptors are stimulated, but have not been used for the monitoring of oculometric response to bone-conducted force stimulation below and above the audible range. 
     Oculometric response data may be captured using techniques other than (or in addition to) video imaging. For example, an electro-oculographic technique may be used, or an induction technique may be used in which the movement of a sensor in physical contact with the eye is measured (e.g., by measuring the currents induced in a coil of an induction oculometer coupled to the eye). 
     The otolithic organs can be stimulated by various types of stimulation, including acoustic, acceleration force, electrical (galvanic) and magnetic. In various embodiments, one or more of these stimulation techniques may be used to stimulate the otolithic organs above or below the audible range for diagnostic purposes. 
     Various examples of the embodiments disclosed herein are discussed in the following paragraphs. 
     Example 1 is an apparatus, including: a housing having a striking end; an impactor disposed proximal to the striking end, the impactor operatively linked to a guide disposed within the housing, the impactor configured to travel from a starting point and a striking point spaced a predetermined distance away from the starting point, wherein the striking point is disposed between the starting point and a point of maximal extension of the impactor; and an electrically driven actuator system, at least partially enclosed within the housing, the electrically driven actuator system configured to cause the impactor to travel from the starting point to the striking point, thereby delivering a mechanical stimuli for transmission to a skull bone; wherein the electrically driven actuator system is configured to controllably decelerate the impactor prior to the impactor reaching the striking point. 
     Example 2 may include the subject matter of Example 1, and may further specify that the housing is longitudinal and forms a handle at a non-striking end distal to the striking end. 
     Example 3 may include the subject matter of any of Examples 1-2, and may further include: a first spring disposed in the housing and arranged to store energy when motion of the electrically driven actuator system causes the impactor to travel to the starting point. 
     Example 4 may include the subject matter of any of Examples 1-3, and may further specify that the electrically driven actuator system comprises an electrically driven actuator connected to the impactor through an inertial mass, the inertial mass being suspended between two opposing springs secured to the housing. 
     Example 5 may include the subject matter of any of Examples 1-4, and may further specify that the electrically driven actuator system is configured to accelerate the impactor along a linear guide. 
     Example 6 may include the subject matter of any of Examples 1-5, and may further specify that the electrically driven actuator system is configured to accelerate the impactor along an angular guide. 
     Example 7 may include the subject matter of any of Examples 1-6, and may further specify that the electrically driven actuator system is configured to controllably decelerate the impactor prior to the impactor reaching the striking point by loading a spring as the impactor moves toward the striking point from the starting point. 
     Example 8 may include the subject matter of any of Examples 1-7, and may further specify that less than 50 decibels Hearing Level of sound is generated when the impactor delivers the mechanical stimuli. 
     Example 9 may include the subject matter of any of Examples 1-8, and may further specify that the electrically driven actuator system is configured to deliver a plurality of mechanical stimuli for transmission to the skull bone, and the plurality of mechanical stimuli includes at least four in a span of less than one second. 
     Example 10 may include the subject matter of any of Examples 1-9, and may further specify that the electrically driven actuator system comprises an electrically driven actuator within the housing, and the housing is a handheld body. 
     Example 11 may include the subject matter of Example 10, and may further specify that the electrically driven actuator system comprises a controller coupled to the electrically driven actuator, and wherein the apparatus further comprises a switch mounted on the handheld body, the switch coupled to the controller and configured to output a trigger signal to the controller to initiate movement of the impactor. 
     Example 12 may include the subject matter of any of Examples 10-11, and may further specify that the electrically driven actuator system comprises a controller coupled to the electrically driven actuator, and wherein the apparatus further comprises a switch that is remote from the housing, communicatively coupled to the controller, and configured to output a trigger signal to the controller to initiate movement of the impactor. 
     Example 13 may include the subject matter of any of Examples 1-12, and may further specify that the electrically driven actuator system comprises a controller coupled to the electrically driven actuator, and wherein the apparatus further comprises a sensor configured to output an electrical signal to the controller when the impactor is proximal to the striking point. 
     Example 14 may include the subject matter of Example 13, and may further specify that the electrical signal triggers a recording of an action potential at a patient, the action potential corresponding to gravitation receptors of an inner ear of the patient. 
     Example 15 may include the subject matter of any of Examples 1-14, and may further specify that the electrically driven actuator system comprises a controller coupled to the electrically driven actuator, wherein the electrically driven actuator system is configured to deliver a plurality of mechanical stimuli for transmission to the skull bone, and wherein the controller directs the electrically driven actuator to deliver a plurality of stimuli until a zero-response action potential is measured. 
     Example 16 may include the subject matter of any of Examples 1-15, and may further include: a frame configured to seat over a portion of a face of the patient; and a plurality of sensing members, each member comprising at least one electrode fixably attached to an arm extending from the frame, the electrode configured to seat over a portion of extraocular muscles, including a portion of an inferior oblique eye muscle, to detect an action potential thereon. 
     Example 17 may include the subject matter of Example 16, and may further specify that the frame forms a pre-defined gap with the extraocular muscles and a globe of the eye so to not exert a pressure thereon. 
     Example 18 may include the subject matter of any of Examples 16-17, and may further specify that the arm is adapted to articulate and adjustably position the electrode to contact skin over the extraocular muscles. 
     Example 19 may include the subject matter of any of Examples 16-18, and may further specify that the electrode is a preamplified electrode. 
     Example 20 may include the subject matter of any of Examples 1-19, and may further include: an upright structural member; a vertically adjustable chin rest fixably mounted to the upright structural member, the chin rest being positioned below a position that causes a patient to lean in and flex his or her neck in such a manner that causes a portion of sternocleidomastoid muscles of the patient to contract; a sensor extending from the upright structural member to seat over the portion of the sternocleidomastoid muscles; and a sensor extending from the upright structural member to seat over the portion of the inferior oblique muscles. 
     Example 21 is a method for assessing vestibular system function, including: stimulating the inner ear with a bone-conducted acceleration force signal; collecting data representative of gravitational receptor-induced ocular motion; and on the basis of the data, evaluating vestibular system function. 
     Example 22 may include the subject matter of Example 21, and may further specify that collecting data includes obtaining a video signal representative of ocular motion. 
     Example 23 may include the subject matter of any of Examples 21-22, and may further specify that collecting data includes obtaining a signal representative of ocular motion. 
     Example 24 may include the subject matter of any of Examples 21-23, and may further specify that collecting data includes obtaining an electro-oculographic signal representative of ocular motion. 
     Example 25 may include the subject matter of any of Examples 21-24, and may further include low-pass filtering the collected data. 
     Example 26 may include the subject matter of any of Examples 21-25, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to a bone-conducted acceleration force having a fundamental frequency below the audible range. 
     Example 27 may include the subject matter of any of Examples 21-26, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to an electrical signal having a fundamental frequency below the audible range. 
     Example 28 may include the subject matter of any of Examples 21-27, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to a head vibration having a fundamental frequency below the audible range. 
     Example 29 may include the subject matter of any of Examples 21-28, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to magnetic stimulation having a fundamental frequency below the audible range. 
     Example 30 may include the subject matter of any of Examples 21-29, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to a bone-conducted acceleration force having a fundamental frequency above the audible range. 
     Example 31 may include the subject matter of any of Examples 21-30, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to an electrical signal having a fundamental frequency above the audible range. 
     Example 32 may include the subject matter of any of Examples 21-31, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to a head vibration having a fundamental frequency above the audible range. 
     Example 33 may include the subject matter of any of Examples 21-32, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to magnetic stimulation having a fundamental frequency above the audible range. 
     Example 34 may include the subject matter of any of Examples 21-33, and may further specify that stimulating the gravitational receptors of the vestibular system includes exposing the vestibular system to a signal having a fundamental frequency below about 50 Hz. 
     Example 35 may include the subject matter of any of Examples 21-34, and may further specify that collecting data includes collecting data indicative of a direction of ocular motion. 
     Example 36 may include the subject matter of any of Examples 21-35, and may further specify that collecting data includes collecting data indicative of a magnitude of directional ocular motion. 
     Example 37 may include the subject matter of any of Examples 21-36, and may further specify that evaluating vestibular function includes detecting any otic capsule dehiscence, including superior canal dehiscence. 
     Example 38 may include the subject matter of any of Examples 21-37, and may further specify that evaluating vestibular function includes detecting the presence of a third window in the inner ear. 
     Example 39 may include the subject matter of any of Examples 21-38, and may further specify that evaluating inner ear function includes detecting an otic capsule dehiscence, including a perilymph fistula. 
     Example 40 may include the subject matter of any of Examples 21-39, and may further specify that evaluating inner ear function includes detecting endolymphatic hydrops. 
     Example 41 may include the subject matter of any of Examples 21-40, and may further specify that evaluating vestibular function includes detecting asymmetry of the gravitational receptors by quantitatively measuring oculographic responses. 
     Example 42 may include the subject matter of any of Examples 21-41, and may further specify that evaluating vestibular function includes identifying patients at risk of hospital falls by determining weakness or absence of gravitational receptor function. 
     Example 43 may include the subject matter of any of Examples 21-42, and may further specify that evaluating vestibular function includes detecting the effects of ototoxicity. 
     Example 44 is a system for assessing vestibular function, the system including: an imaging system configured to measure gravitational receptor-induced eye movements; a stimulator configured to generate a bone-conducted acceleration force below audible range stimulus of the otolithic organs; and a data processing system in communication with the imaging system and the stimulator, the data processing system being configured to analyze gravitational receptor-induced eye movement. 
     Example 45 may include the subject matter of Example 44, and may further specify that the imaging system includes a video camera. 
     Example 46 may include the subject matter of any of Examples 44-45, and may further specify that the imaging system includes an induction oculocometer capable of measuring responses following induction of otolithic stimulation. 
     Example 47 may include the subject matter of any of Examples 44-46, and may further specify that the stimulator includes a bone-conducted acceleration force signal source. 
     Example 48 may include the subject matter of any of Examples 44-47, and may further specify that the stimulator includes an electrical signal, e.g., galvanic, source. 
     Example 49 may include the subject matter of any of Examples 44-48, and may further specify that the stimulator includes a mechanical stimulator for exposing the vestibular system to bone-conducted acceleration force stimulation. 
     Example 50 may include the subject matter of any of Examples 44-49, and may further specify that the stimulator includes a mechanical stimulator for exposing the vestibular system to a head vibration below the frequency of auditory stimulation. 
     Example 51 may include the subject matter of any of Examples 44-50, and may further specify that the stimulator includes a magnetic stimulator for exposing the vestibular system to magnetic stimulation. 
     Example 52 may include the subject matter of any of Examples 44-51, and may further specify that the stimulator is configured to generate a stimulus having an inaudible fundamental frequency below 50 Hz. 
     Example 53 may include the subject matter of any of Examples 44-52, and may further specify that the stimulator is configured to generate a repetitive stimulus having frequency content below the audible range. 
     Example 54 may include the subject matter of any of Examples 44-53, and may further specify that the stimulator is configured to provide repeated pulsatile stimulation having frequency content below the audible range. 
     Example 55 may include the subject matter of any of Examples 44-54, and may further include a filter for filtering data acquired by the imaging system. 
     Example 56 may include the subject matter of any of Examples 44-55, and may further specify that the stimulator includes a mechanical stimulator for exposing the vestibular system to a head vibration above the frequency of auditory stimulation. 
     Example 57 may include the subject matter of any of Examples 44-56, and may further specify that the stimulator is configured to provide repeated pulsatile stimulation having frequency content above the audible range. 
     Example 58 may include the subject matter of Example 55, and may further specify that the filter includes a low-pass filter having a cut-off frequency above 50 Hertz. 
     Example 59 may include the subject matter of Example 58, and may further specify that the low-pass filter includes a Bessel filter. 
     Example 60 is one or more non-transitory computer readable media having instructions thereon that, in response to execution by one or more processing devices of a computing system, cause the computing system to: provide control signals to an apparatus to cause the apparatus to deliver one or more mechanical stimuli for transmission to a skull bone, wherein the apparatus includes a housing having a striking end; an impactor disposed proximal to the striking end, the impactor operatively linked to a guide disposed within the housing, the impactor configured to travel from a starting point and a striking point spaced a predetermined distance away from the starting point, wherein the striking point is disposed between the starting point and a point of maximal extension of the impactor; and an electrically driven actuator system, at least partially enclosed within the housing, the electrically driven actuator system configured to cause the impactor to travel from the starting point to the striking point, thereby delivering a mechanical stimulus for transmission to a skull bone of a patient; wherein the electrically driven actuator system is configured to controllably decelerate the impactor prior to the impactor reaching the striking point. 
     Example 61 may include the subject matter of Example 60, and may further include instructions thereon that, in response to execution by the one or more processing devices of the computing system, cause the computing system to: receive data representative of motion of one or more eyes of the patient, wherein the motion is at least partially in response to the mechanical stimulus delivered to the skull bone; and provide control signals to cause a display device to display an eye motion indicator based on the data representative of motion. 
     Example 62 may include the subject matter of Example 61, and may further specify that less the data representative of motion includes images of the one or more eyes. 
     Example 63 may include the subject matter of Example 62, and may further specify that less the data representative of motion includes video of the one or more eyes. 
     Example 64 may include the subject matter of any of Examples 61-63, and may further specify that less the data representative of motion includes a direction, speed, or magnitude of horizontal, vertical, or torsional eye movement. 
     Example 65 may include the subject matter of any of Examples 60-64, and may further include instructions thereon that, in response to execution by the one or more processing devices of the computing system, cause the computing system to: provide control signals to an image capture device to cause the image capture device to capture images of the one or more eyes; wherein the data representative of motion is based on the captured images. 
     Example 66 may include the subject matter of any of Examples 60-65, and may further specify that the electrically driven actuator system is to deliver a plurality of mechanical stimuli having a fundamental frequency below the audible range. 
     Example 67 may include the subject matter of any of Examples 60-66, and may further specify that the electrically driven actuator system is to deliver a plurality of mechanical stimuli having a fundamental frequency above the audible range. 
     Example 68 may include the subject matter of any of Examples 60-67, and may further specify that the electrically driven actuator system is to deliver a plurality of mechanical stimuli for transmission to the skull bone, and the plurality of mechanical stimuli includes at least four in a span of less than one second. 
     Example 69 may include the subject matter of any of Examples 60-68, and may further specify that the electrically driven actuator system comprises an electrically driven actuator within the housing, and the housing is a handheld body. 
     Example 70 is a system, including: an apparatus, including a housing having a striking end, an impactor disposed proximal to the striking end, the impactor operatively linked to a guide disposed within the housing, the impactor configured to travel from a starting point and a striking point spaced a predetermined distance away from the starting point, wherein the striking point is disposed between the starting point and a point of maximal extension of the impactor, and an electrically driven actuator system, at least partially enclosed within the housing, the electrically driven actuator system configured to cause the impactor to travel from the starting point to the striking point, thereby delivering a mechanical stimulus for transmission to a skull bone of a patient, wherein the electrically driven actuator system is configured to controllably decelerate the impactor prior to the impactor reaching the striking point; and an oculometric response monitoring system including a video camera for capturing video of motion of one or more eyes of the patient, wherein the motion is at least partially in response to the mechanical stimulus delivered to the skull bone. 
     Example 71 may include the subject matter of Example 70, and may further specify that less the oculometric response monitoring system includes logic to process the captured video to determine a direction, speed, or magnitude of horizontal, vertical, or torsional eye movement. 
     Example 72 may include the subject matter of any of Examples 70-71, and may further specify that the video camera is included in a pair of goggles. 
     Example 73 may include the subject matter of any of Examples 70-72, and may further specify that the oculometric response monitoring system includes multiple video cameras. 
     Example 74 may include the subject matter of any of Examples 70-73, and may further specify that less than 50 decibels Hearing Level of sound is generated when the impactor delivers the mechanical stimuli. 
     Example 75 is a method for monitoring a patient, including: causing an apparatus to deliver one or more mechanical stimuli for transmission to a skull bone, wherein the apparatus includes: a housing having a striking end, an impactor disposed proximal to the striking end, the impactor operatively linked to a guide disposed within the housing, the impactor configured to travel from a starting point and a striking point spaced a predetermined distance away from the starting point, wherein the striking point is disposed between the starting point and a point of maximal extension of the impactor, and an electrically driven actuator system, at least partially enclosed within the housing, the electrically driven actuator system configured to cause the impactor to travel from the starting point to the striking point, thereby delivering a mechanical stimulus for transmission to a skull bone of a patient, wherein the electrically driven actuator system is configured to controllably decelerate the impactor prior to the impactor reaching the striking point; and receiving data representative of motion of one or more eyes of the patient, wherein the motion is at least partially in response to the mechanical stimulus delivered to the skull bone. 
     Example 76 may include the subject matter of Example 75, and may further include causing a display device to display an eye motion indicator based on the data representative of motion. 
     Example 77 may include the subject matter of any of Examples 75-76, and may further specify that the data representative of motion includes video of the one or more eyes. 
     Example 78 may include the subject matter of any of Examples 75-77, and may further specify that the electrically driven actuator system is to deliver a plurality of mechanical stimuli having a fundamental frequency below the audible range. 
     Example 79 may include the subject matter of any of Examples 75-78, and may further specify that the electrically driven actuator system is to deliver a plurality of mechanical stimuli having a fundamental frequency above the audible range.