Abstract:
A method of testing hearing automatically selects test ear and test frequencies to produce a diagnostic audiogram providing a plurality of quantitative, examiner-independent measures of test reliability. The method automatically presents appropriate masking noise to a non-test ear. In addition, the method alerts an examiner to thresholds that may be inaccurate due to inappropriate masking or subject inconsistency. A software driven system automatically carries out the method on a test subject.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to provisional application serial No. 60/117,402, filed Jan. 27, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     Clinical testing of hearing sensitivity is usually performed by an audiologist using an audiometer that presents puretone stimuli at controlled frequencies and intensities. The test is performed by manually presenting stimuli according to loosely defined rules. Threshold, the lowest intensity of a stimulus that the listener can hear, is determined for each test frequency, also according to loosely defined rules. The method was first described in clinical publications, Hughson W, Westlake H: Manual for program outline for rehabilitation of aural casualties both military and civilians. Trans. Am. Acad. Ophthalmol. Otolaryngol. Suppl. 48, 1-15, 1944; Carhart R, Jerger J F: Preferred method for clinical determination of puretone thresholds. J.Speech Hear. Dis. 24:330-345, 1959, and later incorporated into a national standard. American National Standards Institute. American National Standard Methods for Manual Pure Tone Audiometry, ANSI S3,21-1978. However many aspects of the procedure are not standardized, such as the number of test stimuli, the temporal characteristics of the stimuli, and the rules for the use of contralateral masking noise. 
     Test results are influenced by a number of uncontrolled procedural and listener factors including the following. 
     The experience of the examiner 
     Shortcuts and methodologic biases of the examiner 
     Intraexaminer procedural variations 
     Interexaminer procedural variations 
     Previous experience of the listener 
     Listener response criterion 
     As a result of less than ideal methodologic control, the accuracy and test-retest reliability are compromised to an unknown extent. This limits the ability to compare test results across examiners and listeners as well as the ability to track changes in hearing sensitivity. 
     SUMMARY OF THE INVENTION 
     The present invention provides an Adaptive Method for Testing Auditory Sensitivity (AMTAS) wherein sensitivity of the auditory system is measured in a manner to reduce the problems associated with routine clinical hearing testing. The present invention, which may be used to replace clinical puretone audiometry in the diagnostic hearing evaluation, selects test ear and test frequency, provides contralateral masking when appropriate, and quantitatively assesses test reliability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an example embodiment of the AMTAS system according to the invention. 
     FIGS. 2 and 3 illustrate example embodiments of the methodology of the invention. 
     FIG. 4 is a flowchart illustrating the method of determining thresholds, L 1 . 
    
    
     DETAILED DESCRIPTION 
     Table 1 lists definitions of terms and symbols used throughout the specification. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Definition of Terms 
               
             
          
           
               
                 TERM (Default Value) 
                 Symbol 
                 DEFINITION 
               
               
                   
               
               
                 Subject 
                 S 
                 The person being tested 
               
               
                 Examiner 
                 E 
                 The person administering the test 
               
               
                 Trial 
                   
                 A sequence of temporal intervals corresponding to one 
               
               
                   
                   
                 stimulus presentation 
               
               
                 Ready Interval 
                 I r   
                 The first temporal interval of a trial; the interval preceding 
               
               
                   
                   
                 the stimulus; I r  has a duration d r   
               
               
                 Observation Interval 
                 I o   
                 The temporal interval following the Ready Interval; the 
               
               
                   
                   
                 interval in which the stimulus is presented; I o  has a 
               
               
                   
                   
                 duration d o   
               
               
                 Vote Interval 
                 I v   
                 The temporal interval following the Observation Interval; 
               
               
                   
                   
                 I v  begins at the offset of I o  and ends when the subject 
               
               
                   
                   
                 responds 
               
               
                 Level 
                 L 
                 The level of a stimulus; for auditory stimuli L may be 
               
               
                   
                   
                 specified sound pressure level or hearing level 
               
               
                 Inital Level 
                 L i   
                 L of the first stimulus presentation in a threshold 
               
               
                 (40 dB HL) 
                   
                 determination 
               
               
                 Inital Increment 
                 ΔL i   
                 the amount that L is incremented when a “No” response 
               
               
                 (10 dB) 
                   
                 occurs to L i   
               
               
                 Stimulus Decrement 
                 ΔL d   
                 The amount that L is decremented following a “yes” 
               
               
                 (10 dB) 
                   
                 response 
               
               
                 Stimulus Increment 
                 ΔL ″   
                 The amount that L is incremented following “No” 
               
               
                 (5 dB) 
                   
                 responses that occur after the first “Yes” response 
               
               
                 Maximum Level 
                 L m   
                 The maximum value of L for a specified stimulus 
               
               
                 Criterion Level 
                 L c   
                 L corresponding to a “Yes” response immediately preceded 
               
               
                   
                   
                 by a “No” response 
               
               
                 Threshold Criterion 
                 C 
                 Number of times L c  must occur at a given L to meet the 
               
               
                 (2) 
                   
                 definition of threshold level L t   
               
               
                 Threshold Level 
                 L t   
                 L corresponding to threshold; L at which L c occurs C times   
               
               
                 Number of Stimuli 
                 N s   
                 Number of stimulus presentations requires to determine L t   
               
               
                 Masking Criterion 
                 M 
                 In the masking mode, minimum L for which masking is 
               
               
                 [See Table 3] 
                   
                 presented to the non-test ear 
               
               
                 Interaural Attenuation 
                 IA 
                 The estimated difference in stimulus level in the test ear 
               
               
                 [See Table 3] 
                   
                 and non-test ear 
               
               
                 Masker Level 
                 ML 
                 The level of the masking noise (in effective masking level) 
               
               
                   
                   
                 presented to teh non-test ear 
               
               
                 Masker Level at 
                 ML t   
                 The level of the masking noise (in effective masking level) 
               
               
                 Threshold 
                   
                 presented to the non-test ear when the test signal level is L t   
               
               
                 Test-Retest Difference @ 
                 ΔT 1k  or 
                 Difference L t  for two 1-kHz or 0.5 kHz threshold 
               
               
                 kHz or 0.5 kHz 
                 ΔT 0.5k   
                 measures 
               
               
                 Catch Trial 
                   
                 A trial for which the observation interval contains no 
               
               
                   
                   
                 stimulus 
               
               
                 Catch Trial Probability 
                 P c   
                 The probability that a trial will be a catch trial 
               
               
                 (20%) 
               
               
                 False Response 
                 P y   
                 Proportion of “Yes” responses in Catch Trials; determined 
               
               
                 Probability 
                   
                 for each test stimulus 
               
               
                 Feedback 
                   
                 Information provided to S indicating that a “Yes” vote 
               
               
                   
                   
                 occurred during a catch trial 
               
               
                 Octave Threshold 
                 D 
                 Difference between adjacent octave frequencies above 
               
               
                 Difference Criterion 
                   
                 which the interovtave frequency is tested. 
               
               
                   
               
             
          
         
       
     
     FIG. 1 is the preferred embodiment of AMTAS system  10 . System  10  includes computer  12  connected to digital signal processor (DSP)  14  via line  16 , transducer  18  connected to DSP  14  via line  20 , transducer  22  connected to DSP  14  via line  24 , yes button  26  and no button  28  are connected to computer  12  through line  30  and line  32 , respectively, and line  34  connects panel  36  to computer  12 . Panel  36  further includes get ready light  38 , listen now light  40 , vote now light  42 , and false alarm light  44 . 
     In operation, an examiner (E) presents instructions either verbally or in writing to a subject (S) as follows: 
     You are going to hear some tones. Most of them will be very soft. The tone may be in either ear. When the tone occurs it will always be while the “Listen Now” light is on. When the “Vote Now” light comes on, I want you to tell me if you think there was a tone when the “Listen Now” light was on. Push the YES button if you think there was a tone. Push the NO button if you did not hear a tone. You must push the YES button or the NO button when the “Vote Now” light comes on. The “False Alarm” light will come on if you pushed the YES button when there was no tone. You may hear some noise that sounds like static. If you hear a noise, ignore it and only push the YES button if you hear a tone. Do you have any questions? 
     Transducers  18  and  22  are placed on or behind S&#39;s ears. Thereafter, no intervention by E is required. Software installed in computer  12  carries out S&#39;s hearing test automatically. 
     Threshold levels, L t , are determined for each of a set of air- and/or bone-conducted auditory stimuli, which E specifies. Stimuli are puretones of varying frequency. Test frequencies are selected from those in Table 2. Frequencies shown in italics are default test frequencies. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 (13) Test Frequencies (kHz) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Air 1   
                 0.125 
                 
                   0.25 
                 
                 
                   0.5 
                 
                 0.75 
                 
                   1.0 
                 
                 1.5 
                 
                   2.0 
                 
                 3.0 
                 
                   4.0 
                 
                 6.0 
                 
                   8.0 
                 
               
               
                 Bone 2   
                   
                 
                   0.25 
                 
                 
                   0.5 
                 
                 0.75 
                 
                   1.0 
                 
                 1.5 
                 
                   2.0 
                 
                 3.0 
                 
                   4.0 
                 
               
               
                   
               
               
                 Default frequencies are shown in italics.  
               
               
                   a Air refers to air-conduction testing  
               
               
                   2 Bone refers to bone-conduction testing  
               
             
          
         
       
     
     E may use the default set of stimuli or another set of stimuli that E has selected from the frequencies in Table 2. The default set includes audiometric frequencies that are required for a diagnostic hearing evaluation and additional frequencies are automatically tested when needed. 
     Each stimulus is presented in a trial, which is illustrated in FIG.  2 . Trial structure  50  consists of Ready Interval (I r )  52  of duration d r , Observation Interval (I o )  54  of duration d o , followed by Vote Interval (I v )  56  of variable duration. 
     The testing is performed using a psychophysical method, which is an adaptive Yes/No procedure. The stimulus is presented during I o    54 . S responds during I v    56  by pushing Yes Button  18  if a stimulus was detected during I o    54  or No Button  22  if no stimulus was detected in I o    54 . I v    56  ends when S responds. Catch trials, trials in which no stimulus is presented in I o , are performed randomly with a predetermined probability, P c , to determine S&#39;s reliability. Feedback is used to inform S when a “Yes” response occurred during a catch trial. False Alarm light  44  lights when S presses Yes button  26  during each catch trial. 
     The rate of stimulus presentation is determined by S&#39;s response time, allowing S to control the pace of the test. This permits testing of subjects with a wide range of age, cognitive ability, reaction time, and motor dexterity. Trials are presented repetitively at various stimulus levels L until L t  is determined. The process is repeated for all E-specified stimuli or the default stimulus set. 
     FIG. 3, consisting of flowchart  60 , illustrates the logic for the selection of test frequency and test ear for air-conduction testing using the default stimulus set. The default initial test ear for air-conduction testing is the right ear. L t  at 1 kHz is determined for the right ear and then for the left ear. The test ear for subsequent stimuli is the ear with the better L t  at 1 kHz. For air-conduction testing, the default order of test frequencies is the following: 1 kHz, 2 kHz, 4 kHz, 8 kHz, 0.5 kHz, and 0.25 kHz. Interoctave frequencies (0.75 kHz, 1.5 kHz, 3 kHz, and 6 kHz) are automatically tested when the difference between two adjacent octave frequencies exceeds D, where D is a predetermined value. The default value of D is 20 decibels (dB). After L t  is determined for all frequencies, the test is repeated at 1 kHz unless L t &gt;L m , where L m  is the maximum value of L for a specified stimulus, in which case 0.5 kHz is retested. The difference in the two 1 kHz thresholds, ΔT 1k  (or 0.5 kHz, ΔT 0.5k ), is a measure of test reliability. After thresholds are tested for each selected frequency, the other ear is tested. 
     After air-conduction testing is completed, E is prompted to place the bone-conduction transducer behind the ear with the poorer L t  at 1 kHz (or 0.5 kHz). An earphone is placed over the non-test ear for masking, which is explained below. If the default bone-conduction stimulus set is selected, the frequencies are tested in the following order: 1 kHz, 2 kHz, 4 kHz, 0.5 kHz, and 0.25 kHz. After all frequencies are tested, E is prompted to reverse the transducer and the other ear is tested. 
     When the test signal may be audible in the non-test ear, a masking signal is automatically presented to ensure that perception of the test signal by the non-test ear does not affect the test. When testing with air-conducted stimuli, masking is presented to the non-test ear in I o  when L&gt;M, where M is the masking criterion. M is the level at which the stimulus may be audible in the non-test ear of a normal hearing subject for a given stimulus/transducer combination. The masking level, ML (in effective masking level), presented to the contralateral ear is L−IA+10 dB where IA is the average interaural attenuation. M and IA are dependent on the stimulus and the transducer. The M and IA values in Table 3 may be used for two commonly used audiometric transducers. When testing with bone-conducted stimuli, the non-test ear is always masked. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 (20) Interaural Attenuation and Masking Criteria 
               
             
          
           
               
                 Transducer 
                 Freq (kHz): 
                 0.125 
                 0.25 
                 0.5 
                 0.75 
                 1.0 
                 1.5 
                 2.0 
                 3.0 
                 4.0 
                 6.0 
                 8.0 
               
               
                   
               
             
          
           
               
                 TDH-50 
                 
                   IA 
                   1 
                 
                 40 
                 40 
                 40 
                 40 
                 40 
                 40 
                 45 
                 45 
                 50 
                 50 
                 50 
               
               
                   
                 
                   M 
                 
                 30 
                 30 
                 30 
                 30 
                 30 
                 30 
                 35 
                 35 
                 40 
                 40 
                 40 
               
               
                 ER-3A 
                 
                   IA 
                   2 
                 
                 75 
                 75 
                 75 
                 75 
                 70 
                 55 
                 50 
                 50 
                 50 
                 50 
                 50 
               
               
                   
                 
                   M 
                 
                 65 
                 65 
                 65 
                 65 
                 60 
                 45 
                 40 
                 40 
                 40 
                 40 
                 40 
               
               
                 Bone Cond 
                 
                   IA 
                 
                   
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
                 
                   M 
                 
                   
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
               
                   1 Average IA-5dB  
               
               
                   2 Average IA-10dB  
               
             
          
         
       
     
     FIG. 4 illustrates an example embodiment of the steps in determining L t  by adaptively varying L. L t  is the lowest level at which S hears a tone at least 50% of the time. Adaptive method  70  of FIG. 4 includes Initial step  72 , Increment step  74 , Maximum Threshold step  76 , Catch trials  78  and  80 , Decrement step  82 , Catch trials  84  and  86 , Increment step  88 , and C Value step  90 . 
     In operation, the initial stimulus, L i , is presented to S at Initial step  72 . If S responds “No” to L i , L of the next stimulus is presented at L+ΔL i  at Increment step  74 . Increment step  74  is repeated by incrementing L by ΔL i  until a “Yes” response occurs or until L=L m . If L reaches L m  then L t &gt;L m . 
     If S responds “Yes” to L i , Catch trial  78  is performed to provide an indication of S&#39;s reliability. If S responds “Yes” to Catch trial  78 , then False Alarm light  44  illuminates (see FIG. 1) and Catch trial  80  is performed. Regardless of S&#39;s response to Catch trial  80 , testing continues. If, however, S responds “No” to Catch trial  78 , testing continues without performing Catch trial  80 . 
     When testing continues, L of the next stimulus is presented at L−ΔL d  at Decrement step  82 . After each “Yes” response, Catch trials  78  and  80  are performed again, and L is subsequently decremented by ΔL d . If S responds “No” at Decrement step  82 , Catch trials  84  and  86  are performed as described above for Catch trials  78  and  80 . For each “No” response after the first “Yes” response at Decrement step  82 , L is incremented by ΔL u , which is shown at Increment step  88 . 
     L that produces a “Yes” response immediately preceded by a “No” response is designated L c . When L c  occurs C times at the same value of L, where C is the threshold criterion, that level is designated L t . This is illustrated by C Value step  90 . The default value of C is 2, but E can set C to be any value. 
     The number of stimulus presentations, N 1 , required to determine L t  is a quality indicator. Adaptive method  70  is repeated for each E-selected stimulus or for the default stimulus set. 
     The proportion of “Yes” votes following Catch trials  78 ,  80 ,  84 , and  86 , designated P y , is a measure of response reliability. P y  is determined for each L t  and an average P y  is reported for each ear and for both ears combined. 
     After determination of air- and bone-conduction thresholds, system  10  determines threshold measurements for which masking levels may not have been appropriate. These are Masking Alerts. E is prompted to retest those thresholds, and appropriate masker levels are automatically selected. Examples of Masking Alerts are given in Table 4. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Masking Alerts 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 AIR CONDUCTION 
                 ML t  ≦ air conduction L t  of non-tested ear 
               
               
                   
                 ML t  ≦ bone conduction L t  of non-tested ear 
               
               
                 BONE CONDUCTION 
                 ML t  ≦ air conduction, L t  of non-tested ear 
               
               
                   
                 ML t  − IA ≧ bone conduction L t  of test ear 
               
               
                   
               
             
          
         
       
     
     Results are presented in standard audiogram format. The quality indicators listed in Table 5 are reported. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Quality Indicators 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 P y (f) 
                 False alarm probability at each test frequency 
               
               
                 P y (ear) 
                 False alarm probability for ear. 
               
               
                 P y (S) 
                 False alarm probability for both ears combined 
               
               
                 N t (f) 
                 Number of trials required to determine L t  for each 
               
               
                   
                 frequency 
               
               
                 ΔT 1k  or ΔT 0.5k   
                 Test-retest difference at 1 kHz or 0.5 kHz 
               
               
                   
               
             
          
         
       
     
     For each threshold measurement, two quality indicators are reported, P y  and N t . In addition, P y  is reported for each ear and both ears combined. ΔT 1k  or ΔT 0.5k is also reported. Values of each quality indicator that exceed two standard deviations beyond the mean are identified. ML t , the masker level at threshold, is reported for each threshold and Masking Alerts are identified. 
     System  10  and the corresponding method for adaptively testing auditory sensitivity selects a test ear and test frequency, provides contralateral masking when appropriate, and quantitatively assesses test reliability. System  10  and the corresponding method are designed to eliminate the major sources of human error that influence the accuracy of manual purtone audiometry. A summary of the unique features of system  10  and the method contrasted with manual puretone audiometry are presented in Table 6. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 AMTAS Features Contrasted to Manual Puretone Audiometry 
               
             
          
           
               
                 MANUAL PURETONE 
                   
               
               
                 AUDIOMETRY 
                 AMTAS 
               
               
                   
               
               
                 Requires continous control by E 
                 No intervention by E required 
               
               
                 E selects test ear and test frequencies 
                 Test ear and test frequencies automatically selected to 
               
               
                   
                 produce complete diagnostic audiogram 
               
               
                 Provides only qualitative assessment of test 
                 provides five quantitative, E-independent measures 
               
               
                 reliability which is highly dependent on E&#39;s 
                 of test reliability 
               
               
                 experience 
               
               
                 Requires E to determine the need for 
                 Automatically presents appropriate masking noise to 
               
               
                 masking the non-test ear and to manually 
                 non-test ear 
               
               
                 select masker levels 
               
               
                 Does not identify thresholds that are likely 
                 Alerts E to thresholds that may be inaccurate due to 
               
               
                 to be inaccurate 
                 inappropriate masking or subject inconsistency 
               
               
                   
               
             
          
         
       
     
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.