Random pattern tracking acceleration tolerance tester

A G force acceleration effects monitoring apparatus involving a pair of LED or other visual stimulus arrays, one randomly patterned by an electronic driving apparatus and one patterned by the manipulation of a G force test subject. The electronic driving apparatus preferably includes a sum of sines algorithm and the test subject manipulations are received preferably from a joystick controller. Mounting of the apparatus in a centrifuge gondola and also in off-line training stations and use of the invention by animals are also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to the field of G force acceleration effect sensing 
accomplished by way of visual field and psychomotor tracking performance 
evaluation in a test subject. 
When a human subject is exposed to increasing G force acceleration, a 
well-established sequence of degradation changes in the subject's blood 
circulation occur. In modern high-performance aircraft and spacecraft, 
these hemodynamic changes require consideration in order that a human 
operator remain physically able to function as an aircraft pilot or as a 
performer of technical functions. The change in human blood circulation is 
particularly severe in the case of +GZ axis G forces, forces directed 
downward from the head and tending to collect blood in the lower 
extremities of a subject's torso so that the blood supply to the brain and 
eye retina are diminished. Another severe condition results from -GZ axis 
acceleration forces which tend to collect excessive blood quantity and 
pressure in the brain and produce a red-out response. Supplemental body 
pressure apparatus and test subject physical "exercises" which tend to 
increase the tolerance of acceleration forces have been used in military 
equipment for some time; the G-suit is a well-known example of such 
apparatus and is particularly effective for increasing the tolerance of 
+GZ axis forces. G force acceleration in the other coordinate directions, 
that is, along the X axis, tending to press a test subject more firmly 
against a seat back or along the +Y axis, tending to move the subject to 
his left, are also detrimental to blood circulation to lesser degrees. 
The progressive reduction of blood circulation particularly in response to 
increasing GZ forces results in several correspondingly progressive 
physiological effects, including a dimming of the subject's vision or 
"gray-out", a narrowing of the subject's visual field or vision tunneling, 
a total loss of vision or "blackout" and ultimately a loss of 
consciousness. 
As a result of differences between the intra-ocular pressure and 
intracranial pressure in a human body, blood circulation to the eye is 
diminished prior to circulation to the brain, and a loss of vision, 
particularly far peripheral vision, generally precedes loss of 
consciousness in a G force test subject. This established order of 
circulatory disruption therefore provides a convenient and repeatable 
means by which a test subject's response to G forces can be objectively 
evaluated and by which the onset of undesirable effects in a test subject 
can be detected. 
Exposure to G force acceleration is also known to degrade a test subject's 
psychomotor tracking performance in addition to the above-described 
circulatory or hemodynamic effects. The ability of a test subject to 
perform a task requiring both visual and psychomotor capabilities is 
therefore a doubly useful tool in assessing the degree of tolerance the 
subject exhibits to acceleration G forces. The combination of visual and 
psychomotor capability can therefore be desirably evaluated in a G force 
test environment by assigning a test subject to perform tasks which 
involve visual input and motion output; preferably the expected 
performance should allow measuring both the extent and the rate of 
degradation in the subject's visual field and psychomotor tracking 
ability. 
Arrangements for combining a measurement of a test subject's visual field 
and psychomotor tracking ability under the influence of acceleration G 
forces are known in the art as is evidenced, for example, by the patent of 
Malcolm Cohen, U.S. Pat. No. 4,421,393 and the several G force effect 
measuring systems therein described. 
The Cohen invention concerns a visual field perimeter and psychomotor 
tracking performance measuring apparatus for use with a human test subject 
centrifuge operated by the U.S. Navy. In the Cohen invention a 
semicircular array of light emitting diodes (LEDs) is arranged to subtend 
the lateral field of view of the test subject and is excited such that 
pairs of opposed diodes symmetrically located about a central viewing axis 
are sequentially illuminated at a programmed rate and in an inward or 
outward progressing sequence. The test subject in the Cohen apparatus 
employs a control stick to generate a nulling signal that maintains a 
desired peripheral field pair of light emitting diodes illuminated. The 
Cohen apparatus relies upon the test subject performing a manipulation of 
the control stick in response to peripheral vision diminishing with 
increased acceleration forces. The Cohen apparatus also contemplates the 
use of a pseudo-random pattern of LED excitation without, however, 
specifying the precise nature of the random signal or indicating how it is 
generated. 
A conceptual advantage of the present invention over the Cohen apparatus 
concerns the achieved reduction in the ability of a test subject to 
bravado, enhance or cheat the measurement system by artificially 
indicating a better response to the G force effects than he actually 
experiences. In the present invention, the test subject is required to see 
the position of the driving visual stimulus in order to position a 
responding visual stimulus properly. In the absence of seeing the driving 
visual stimulus, the test subject is precluded from making any response 
and thus from enhancing his measured tolerance of the G force. 
The Cohen patent also describes several prior art visual testing 
arrangements including one in which a lamp located in the test subject's 
visual periphery is randomly illuminated and the test subject is required 
to immediately press a button to extinguish the lamp. As indicated in the 
Cohen patent, this arrangement does not test the subject's visual field 
and the rate at which it collapses, nor does it measure the psychomotor 
tracking ability of the subject. 
Additional distinctions of the present invention over the Cohen apparatus 
concern arrangement of the display in the present invention, including the 
two arrays of visual stimulus elements and the circuitry used for driving 
display LED elements. 
Another example of prior patent art relating somewhat to the present 
invention is found in the patent of C.L. Kuether et al, U.S. Pat. No. 
4,255,022, concerning an improved "perimeter" apparatus of the type used 
for vision testing in a medical examination environment. In the Kuether 
invention microprocessor techniques are employed to improve an existing 
perimeter device through incorporation of an electronically-controlled 
silent shutter and an electronically controlled operator lead-through 
system. The Kuether apparatus is of course unconcerned with testing for 
the effects of G force acceleration. 
An example of prior art apparatus requiring the cooperation of a subject 
with a visual stimulus-generating machine is found in the patent of David 
J. Hall, U.S. Pat. No. 4,169,592 wherein there is described an electronic 
reflex challenging game requiring a player to respond to a randomly 
actuated one of three possible light bulbs within an increasingly 
shortened response time. The Hall apparatus is unconcerned with the 
player's physical environment and additionally involves only a race 
against time as the physical trait to be measured in the test subject. 
Another example of prior patents concerning visual testing is found in the 
patent of J. R. Lynn et al, U.S. Pat. No. 3,705,003 n which a test subject 
operates a joystick control in response to an unpredictable or random 
sequence visual stimulus display in order to achieve mapping of his vision 
capability. The Lynn apparatus teaches the use of a cathode ray tube 
display which is arranged in a 64.times.64 or higher resolution grid and 
employs a four-bit intensity determining word at each grid location. As 
indicated at column 10, line 34 in the Lynn patent, the test subject is 
expected to move the joystick control in the general direction of the 
bright spot he has observed on the cathode ray tube screen. The Lynn 
apparatus defines a measurement tool called an error sector and determines 
if the test subject's response comes within an allowable number of error 
sectors of the cathode ray tube displayed spot. 
The Lynn apparatus is of course intended for use in a medical testing 
environment in contrast with applicant's environment of acceleration G 
force effect testing; the Lynn apparatus moreover is silent with respect 
to providing feedback to the test subject as to the results of his 
joystick control manipulation. The Lynn apparatus also appears to depend 
on human operator generation of the random data used for test spot 
location. 
Another example of prior art peripheral vision testing apparatus is found 
in the patent of R. J. Beitel, Jr. U.S. Pat. No. 2,316,042 which discloses 
an adjustable perimeter testing device used for medical vision testing and 
employing manually movable mechanical target or visual stimulus member. 
The Beitel apparatus includes the familiar perimeter screen and moving 
target concept, and further contemplates the use of multicolored targets. 
The Beitel apparatus is also intended for use outside the G force 
acceleration testing environment and employs manual positioning of the 
visual stimuli. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a G force effect measuring 
apparatus which produces a true indication of the test subject's physical 
condition. 
Another object of the invention is to provide a G force effect sensing 
apparatus which can be arranged to train a test subject using an off-line, 
low-cost preliminary environment prior to stress phase G force testing. 
Another object of the invention is to provide a G force effect measuring 
arrangement which is highly immune to spoofing or results enhancement by a 
test subject. 
Another object of the invention is to provide a G force effect sensing 
system which incorporates requirements for visual and psychomotor 
performance by the test subject. 
Another object of the invention is to provide an improved acceleration G 
force sensing apparatus of the pursuit display type. 
Another object of the invention is to provide an acceleration G force 
measurement system which is reliable and low in cost. 
Another object of the invention is to provide a G force response measuring 
apparatus which includes a first array of visual stimuli elements 
dispersed around the peripheral view of a test subject, means for 
energizing the first array elements according to a first pattern of 
position and time, a second array of visual stimuli elements also 
dispersed around the peripheral view area of the test subject with each 
second array element being identified with a first array element, means 
controlled by the test subject for energizing the second array element in 
a second pattern which pursues the first pattern, and means for comparing 
the first and second patterns.

DETAILED DESCRIPTION 
In FIG. 1 of the drawings, the acceleration tolerance testing apparatus of 
the present invention is shown incorporated into a centrifuge G force 
acceleration testing apparatus. This type of apparatus is frequently used 
for measuring the capability of a human to withstand and function under 
exposure to the acceleration forces encountered in a modern aircraft or 
spacecraft. The FIG. 1 centrifuge apparatus includes a spherical gondola 
150 which is mounted in a yoke member 140 at the end of a radius arm 141. 
The arm 141 in turn is arranged to rotate about an axis 144 under the 
influence of electric motors or other prime moving apparatus contained 
within a mounting base 146. The yoke 140 is shown cut away at 147 in order 
that details of the spherical gondola 150 including the gondola cutaway 
portion indicated at 148 by visible. The centrifuge includes gondola 
mounting apparatus indicated generally at 142 and 143, by which the 
gondola 150 is movable in several degrees of freedom in order that the 
orientation of the test subject 100 be controlla be and in order that 
combinations of accelerating force, spin, roll and pitch be possible. The 
centrifuge may also include a counterweight 149 which frequently is 
embodied in the form of motors, slip ring assemblies and other mechanisms 
needed in connection with positioning and moving the test gondola 150. The 
FIG. 1 apparatus is shown approximately to size with respect to the size 
of the test subject 100. A centrifuge of this type is frequently arranged 
to achieve acceleration forces as large as 15 times the force of gravity 
(15 Gs), and is usually capable of relatively high rates of acceleration 
onset or decrease. These testing conditions are usually generated by 
electric motors of several hundred horsepower, rotating flywheels and 
other prime mover apparatus. 
The spherical gondola 150 in FIG. 1 is shown oriented approximately in the 
direction providing maximum positive Z-axis acceleration force, indicated 
by the vector 136, to the test subject 100. The vector 136 is shown to be 
the resultant or summation of an acceleration force vector 132 and a 
gravity vector 134. Arrangements wherein the test subject 100 is 
positioned to receive maximum acceleration force along the X- or Y-axes, 
which are indicated at 118 and 120 in FIG. 1, are also frequently employed 
in order to simulate the effects experienced by present-day crew members 
during aircraft takeoff, landing, or rapid turning maneuvers. The gondola 
150 is usually equipped with a test subject seating arrangement 102, head 
restraint apparatus 124, a helmet 123, feet and leg restraint apparatus as 
generally indicated at 130, an exit and entrance door 145, a television 
camera 137 and a joystick control 104. Signals from the TV camera 137 are 
transmitted by way of a cable 138 and slip rings to a monitoring console 
which is not shown. Other slip rings are used to carry electrical energy 
and test signals such as blood pressure and vital signs information 
concerning the test subject 100 to the monitoring console area; these slip 
rings also communicate electrical signals for energizing the light bar 106 
and the joystick control 104. 
Close attention to the physical well-being of the test subject 100 is 
required during use of the FIG. 1 apparatus. A television camera 137, open 
microphone communications and vital signs monitoring are of course 
essential portions of this close attention. An important additional part 
of this attention involves placing the test subject in a closed-loop or 
feedback visual and psychomotor monitoring system by way of the joystick 
control 104 and the light bar 106. The visual and psychomotor ability of 
the test subject are, as indicated above, particularly sensitive 
indicators of acceleration endurance limits and are sufficiently early in 
indicating ability to prevent the onset of hazardous conditions. 
In the past, there has been a notable tendency for test subjects to 
incorporate an element of bravado in their response to light bar sensing 
arrangements which preceded the FIG. 1 apparatus. This response both 
degrades the usefulness of the test data and also introduces an 
undesirable element of hazard in testing of the FIG. 1 type. In these past 
examples, predictability of the pattern displayed by the light bar 106 was 
one factor which allowed the test subject to "fudge", or artificially 
respond to the light stimulus events. 
The light bar 106 in the acceleration tolerance tester apparatus is mounted 
by a hinge 112 which connects to some fixed portion of the gondola 150 
indicated at 114 in order that the light bar 106 can be easily moved up 
and away from the test subject 100 to facilitate entrance and exit of the 
test subject 100. This hinged mounting arrangement includes the detachable 
elements 126 and 128 located along the light bar 106 for additional 
support and convenient detachment. 
As indicated by the two arrays of visual stimulus elements 111 and 113 in 
the light bar 106, the present invention contemplates the use of a double 
array of stimulus elements in order to achieve a more accurate indication 
of the test subject's capability during a FIG. 1 apparatus test. The 
visual stimulus elements 108 and 110 in the arrays 111 and 113 are 
preferably light emitting diodes (LEDs) of two different colors, for 
example, the lower row of elements in the array 111, element 108 etc., may 
be red light emitting diodes, while the upper row of elements, element 110 
etc., may be green light emitting diodes. Although light emitting diodes 
are preferred as embodiments of the visual stimulus elements, other visual 
stimulus element arrangements, including but not limited to, incandescent 
lamps, electromechanical annucator devices, mechanically movable cursor 
members, and light projection arrangements, which might for example 
project images on the interior surface of the gondola 150 and dispense 
with the light bar 106, are within contemplation of the invention. The 
term "visual stimulus element" is therefore intended to be generic to a 
variety of test subject communicating arrangements which may be conceived 
for FIG. 1 type apparatus. 
It should also be understood that the illustrated vertical alignment of the 
visual stimulus elements 108 and 110 is but one possible arrangement for 
elements which are identified with each other, alternate arrangements 
including side-by-side horizontal mounting, the use of concentric light 
emitters, mounting of the stimulus elements on the top and bottom surfaces 
of the light bar 106, and other relationships between the stimulus 
elements are also within contemplation of the invention. 
In the present invention it is contemplated that the uppermost array of 
visual stimulus elements, as typified by the element 110, will be 
energized in some unpredictable or pseudorandom manner from a source of 
the type described below and that the test subject 100 will be instructed 
to manipulate the joystick 104 in order that the visual stimulus elements 
in the lower array, as typified by the element 108, track or follow this 
unpredictable upper array pattern. In the preferred embodiment, for 
example, a pattern involving excitation of two symetrically located light 
emitting diodes in the upper array of the light bar 106 and a movement of 
this symmetric excitation peripherally around LEDs in the light bar upper 
array is to be tracked or duplicated by a lower array pattern of two 
illuminated light emitting diodes positioned by the test subject's 
joystick 104. 
In addition to the described two arrays of colored light emitting diodes or 
other visual stimulus elements, the FIG. 1 apparatus contemplates the 
presence of two third color visual stimulus elements such as two white 
lights at the center 116 of the light bar 106. These center located 
contrasting color stimulus elements provide a fixation point for the test 
subject 100 that has been found useful in helping a subject maintain 
orientation and in providing a reference for peripheral vision events 
occurring in the lower and upper arrays 111 and 113. Preferably the array 
center stimulus elements when embodied as light sources are arranged to be 
constantly illuminated and therefore may be comprised of incandescent 
lamps driven from any convenient energy source. 
The number of elements to be included in each of the lower and upper arrays 
111 and 113 is selectable between the endpoints of having so few elements 
as to provide inaccurate peripheral vision measurement and having too many 
elements resulting in unneeded complexity and test subject confusion. 
Arrays of sixty elements in each 90-degree quadrant of the light bar 106 
have been found a satisfactory compromise between these endpoints. 
According to this arrangement, therefore, adjacent array elements are 
separated by one and one-half degrees of arc originating at the test 
subject's eyes. This one and one-half degree arcuate spacing of the array 
elements was also recommended in the above-cited U.S. Navy patent, U.S. 
Pat. No. 4,421,393. The disclosure of this Navy patent is hereby 
incorporated by reference into the present specification. 
The above-indicated arrangement wherein the test subject responds to a 
random pattern of excitation in the upper light array 113 in FIG. 1 by 
maneuvering the joystick 104 and producing a similar movement pattern, or 
tracking, in the lower array 111 is identified as a special case of a 
pursuit display, as contrasted with a compensatory display. Compensatory 
displays are characterized by displaying only the error or difference 
between the forcing function signal and the response signal, while a 
pursuit display contains an indication of both the target and the response 
signals in separate display arrays. The U.S. Navy Cohen apparatus 
discussed above is, of course, a compensatory display, since only the 
difference between the target and joystick signals is displayed. A pursuit 
display provides more information to the test subject and those who 
monitor his response. Pursuit displays also add cognitive information to 
the man-machine system, that is, perception, recognition, and awareness 
are required of the test subject during G stress phases of an experiment 
by this form of display. The tracking performance which occurs from human 
subjects using a compensatory and a pursuit display is substantially 
different and is described in the textbook Man-Machine Systems, which is 
incorporated herein below. Since much of the response used in flying an 
aircraft or driving an automobile relate to pursuit rather than 
compensatory tracking, this form of display offers some realism advantage 
to a test environment. 
In FIG. 2 of the drawings there is shown a conceptual arrangement for 
energizing the light bar 106, including the arrays 111 and 113 in FIG. 1. 
The FIG. 2 diagram includes only a representative number of visual 
stimulus elements 202, it being understood that the sixty elements per 
90-degree quadrant, or one and one-half degree arcuate spacing is 
preferred in a practical embodiment of the invention. In FIG. 2 the 
complete light bar assembly is indicated at 200 and illuminated LED or 
actuated visual stimulus elements in this assembly are indicated by the 
letters G and R at 206, 208, 214, and 216; the LEDs 208 and 214 are in the 
lower red array which is controlled by the test subject's joystick 242 and 
the LEDs 206 and 216 are in the upper green array which is controlled by 
the random signal source 222. The array center white lights are indicated 
at 210 and 212 in FIG. 2. A source of energy such as a battery 232 is 
indicated at 240 and 234 as being connected to the white lights. The 
connections 228 and 238 in FIG. 2 indicate connection of the random signal 
source 222 to the upper green array elements while connections 226 and 236 
indicate connection of the test subject's joystick control 242 and its 
associated potentiometer(s) 224 to the lower red array. 
At 218 and 220 in FIG. 2 are indicated the visual field angle, A, and an 
error angle, B, relating to a test subject viewing point 230. The visual 
field angle 218 for a normal person is on the order of 216 degrees, that 
is, a normal person has been found to have far field peripheral vision 
which extends slightly behind a hypothetical straight line extending 
across the front of his eyes. By way of example, a G force test subject is 
found to incur peripheral vision loss or peripheral light loss (PLL) under 
the influence of G force acceleration which reduces this 216 degree visual 
field to 50 degrees or less. PLL is arbitrarily defined as a condition 
existing when the test subject's central visual angle is less than 50 
degrees. 
For some positionings of a test subject with respect to the axis of 
rotation 144 in FIG. 1, the loss of peripheral vision is asymmetric in 
nature, that is, the peripheral vision in one eye may be diminished more 
than that of the other eye; this occurs most notably when the test subject 
is positioned to receive acceleration G force along the Y-axis 120 in FIG. 
1. The contemplated symmetric excitation of the LEDs around the array 
center white lights, as indicated in FIG. 2 of the drawings allows a test 
subject to recognize a report such asymmetric visual capability. 
The error angle 220, B in FIG. 2 may arise from a transient condition 
wherein the test subject has not yet had sufficient time to bring the 
joystick controlled red lower array LEDs into conformance with a newly 
occurring green upper array condition, such transient errors frequently 
persist for about 200 milliseconds and are ultimately corrected by the 
test subject. Angular errors 220 may arise from a more permanent loss of 
ability by the test subject and are to be thusly considered in scoring or 
evaluating the test subject's tolerance of the stress phase. For scoring 
purposes a root means square computation of the error angle B, 220, has 
been found useful. Such computation can be achieved through use of the 
relationship. 
##EQU1## 
where e.sub.t is the error signal angle, N is the number of samples of 
e.sub.t during the time period of interest and e.sub.RMS is the computed 
value of error angle B, 220 weighted for time. The time weighted error 
angle is usable for comparison scoring purposes. Signals for use in the 
monitoring console area and in performing the scoring computations are 
provided at 248 and 250 in FIG. 2. 
Several circuit arrangements are feasible for achieving the desired 
operation of the preferred LED elements in the FIG. 2 apparatus. One 
portion of these circuit arrangements includes the simultaneous excitation 
of symmetrically located LED elements and can be conveniently provided by 
connecting symmetrically located LED elements in electrical series or 
alternately in electrical parallel using of course current limiting 
resistors for each LED element or element pair as shown in FIG. 3 of the 
drawings and described below. 
A plurality of possible embodiments for the random signal source 222 are 
feasible. One such embodiment, for example, might employ a random access 
memory (RAM) loaded with a table of appropriate numerical values with 
either the memory contents or the memory accessing being random in nature. 
It should be noted with respect to the random signal source 222 that a 
pure random excitation of LED elements would provide some excitation 
periods and transition periods which would be undesirably short or 
conversely, undesirably long in duration; the desirable algorithm for the 
random signal source 222 is therefore of a pseudo-random nature wherein 
the transitions are of a human trackable nature. 
Another embodiment of the random source 222, one that is in fact preferred, 
involves the use of a sum of sines algorithm. In order for such a 
sinusoidal-based forcing or driving function to appear random to the human 
subject, the preferred LED driving function is composed of a minimum of 
five sine waves of different frequencies and is arranged to have zero mean 
over the duration of an experiment stress phase (each sine wave repeats 
itself an integral number of periods over the duration of the stress 
phase) with each sine wave having a differing initial phase angle. In the 
textbook Man-Machine Systems by T. B. Sheridan and W. R. Ferrell, which is 
hereby incorporated herein by reference, it is shown empirically that if 
five or more different sine waves are added together in this manner, then 
a human subject is not able to predict the periodic behavior of the 
resulting signal. In general, therefore, the length of the G force test 
run in seconds may be made equal to two periods of the lowest frequency 
sine wave, called the fundamental, to be employed. This fundamental 
frequency would be 1/10 Hz for a 20 second G force stress period, for 
example. The five component sine wave frequencies may be then made prime 
number multiples of this fundamental frequency in order to achieve the 
condition that no two frequencies can ever be integer multiples of each 
other. 
The sum of sines LED forcing function algorithm then operates in accordance 
with the mathematical equation. 
##EQU2## 
In this equation V.sub.1 is the output signal which is decoded or 
threshold detected to determine the on-time of green array LEDs, for 
example. The term a.sub.o in the V.sub.1 equation represents a DC voltage 
chosen to maintain a pair of green LED elements in the "on" condition to 
cover a field of view of at least 50.degree. of the test subject. The 
summation from i=1 to i=n indicates the presence of several sine waves, 
five sine waves being a preferred arrangement. The term a.sub.i is a 
constant determining the relative peak amplitudes of the selected 
component sine waves and their amplitude with respect to the component 
a.sub.o, the a.sub.i term may be different for each of the component sine 
waves. The term W.sub.i t in the V.sub.1 equation identifies the 
frequency of each sine wave component and the term .phi..sub.i determines 
the relative phasing of the individual sine wave components. 
According to this visual stimulus energization arrangement, the green 
lights oscillate in the periphery of the test subject's eye and the 
subject must track the border of these lights using the pair of red lights 
to align with the green lights. The voltage a.sub.o in the above equation 
determines the peripheral light loss angle and the dark to green 
oscillations occur about this voltage value. If the subject cannot see in 
the periphery, he also, of course, is incapable of tracking the green 
lights. Since the subject is instructed to stare straight ahead, he cannot 
claim to see in his periphery if he does not cause the pair of red lights 
to follow the pair of oscillating green lights. Thus, the invention 
provides a true empirical measure of whether a test subject can actually 
see in the periphery rather than relying on subjective comments which may 
be biased or in error. 
A preferred arrangement for generating the sum of sines LED driving 
function involves the use of a digital computer which is programmed in 
accordance with the above-described concepts. Such a computer can be the 
type PDP-11 manufactured by Digital Equipment Corporation (DEC) of Boston, 
Mass. A listing of a FORTRAN IV program capable of generating the sum of 
sines driving function is shown at the end of this specification. Other 
program arrangements and other driving function arrangements can, of 
course, be fabricated within the contemplation of the invention. 
The desired arrangement for causing the green lights to go on in relation 
to the magnitude of the voltage V.sub.1 is believed to be understood, but 
will now be briefly described. If V.sub.1 is at its maximum voltage, the 
furthest pair of LED lights in the periphery are desirably in the "on" 
condition. If V.sub.1 =O, only the center white light remains on. For a 
voltage between V.sub.1 max and O volts, the pair of lights that go on are 
symmetrical about the center white light and their distance from the 
center is proportional to the voltage V.sub.l. For example, in FIG. 5, if 
V.sub.1 =(1/60) V.sub.max, and V.sub.max =10 volts, the pair of green 
lights illuminated is based on the number V.sub.1 /V.sub.max 
(60).apprxeq.l, or the first light on each side of the center light is to 
be energized. If V.sub.1 =(2/3) V.sub.max, then the pair of green lights 
illuminated is based on 2/3 (60)=the fortieth lights. Thus, the center 19 
lights are not illuminated, but the pair of lights a distance 20 from the 
center are illuminated along with the center reference light. The manner 
in which the red lights are driven from the voltage developed by the test 
subject manipulated joystick follows in a similar relationship as for the 
green lights. When the joystick is in the zero position, the potentiometer 
arm voltage is zero volts and only the reference light in the center is 
lit. When the maximum voltage (e.g., 10 volts) is used from the joystick 
potentiometer, the outside pair of lights and the reference light will be 
energized. As in the random excited green array, the distance of the 
energized red array pair from the center is proportional to the voltage 
obtained from the potentiometer arm. 
Electronic circuitry capable of converting the V.sub.1 voltage signal 
provided by either the sum of sines algorithm or the random number 
algorithm or the V.sub.JS joystick potentiometer signal into signals 
capable of energizing light emitting diode (LED) elements is known in the 
electronic circuit art. Essentially such circuitry involves a voltage 
discriminating arrangement wherein one symmetrically located pair of LED 
elements is illuminated for each value of the V.sub.1 signal indicated at 
246 in FIG. 2. In similar fashion such voltage discriminating circuitry 
can also be used to illuminate one symmetrically located pair of LED 
elements in response to each possible value of the joystick output signal 
V.sub.JS, 244 in FIG. 2. Generally, voltage discriminating circuitry of 
this type may be fabricated around an operational amplifier threshold 
sensing circuit or around a digital logic circuit arrangement, examples of 
each of these circuits are shown in FIGS. 3 and 4 of the drawings. 
The FIG. 4 voltage discriminating circuit employs a number of bipolar NPN 
transistors 400-410 for sensing the relative polarities between the 
V.sub.1 or V.sub.JS signals and a pair of reference signals V.sub.LT and 
V.sub.UT, these signals being received on busses 482, 480 and 478. The 
signals on these busses may be obtained from appropriate sources such as 
the joystick potentiometer and the sum of sines generator 224 and 222 in 
FIG. 2 in the case of the V.sub.1 or V.sub.JS signal and from adjustable 
potentiometers for the V.sub.LT and V.sub.UT signals. These bus signals 
may also be increased as to load driving ability through the use of 
suitable buffering amplifiers. 
Operation of the FIG. 4 circuit is based on the concept that conduction in 
the transistor 402, for example, occurs when the V.sub.1 signal is more 
positive than the V.sub.UT signal and similarly, conduction occurs in the 
transistor 400 when the V.sub.1 signal is less positive than the V.sub.LT 
signal. Conduction in the transistors 400 and 402 causes their collector 
output voltages to be in the low level condition and these low level 
signals are received at a NOR gate 416 and provide a high level signal 
output therefrom to energize the two light emitting diodes 418 and 420. If 
either of the transistors 400 and 402 depart from the conducting condition 
because of a change in the relative polarity of the V.sub.1 signal with 
respect to the V.sub.LT or V.sub.UT signals, the output of the NOR gate 
416 will change to the low level condition and the two light emitting 
diodes 418 and 420 will be extinguished. 
Current level and light intensity in the LED elements is determined by the 
value of the resistors 434 and 436 and the output signal level of the NOR 
gate 416. The voltage divider resistor elements 460-474 in FIG. 4 provide 
a means for adjusting the value of the reference signal period to the 
successive pairs of transistors 404 and 406, 408 and 410 in order that 
each of the LED pairs 418 and 420, 422 and 424, and 426 and 428 be 
responsive to differing levels of the V.sub.1 or V.sub.JS signals. 
As indicated by the parallel connection of the LED elements 418 and 420 and 
the series connection of the LED elements 422 and 424 either of these 
connection arrangements is feasible for two symmetrically placed LEDs in 
the light bar assembly. The series resistors 438, 442, 446, 450, 454 and 
484 control the base current in the transistors 400-410 in a manner known 
in the art. The collectors of these transistors are connected to a 
collector voltage supply, which in the FIG. 4 circuit should be positive 
in polarity, by means of collector load resistors 440, 444, 448, 452, 456 
and 486 as is also known in the art. Since the output signal from the 
transistors 400, 402 etc. during the transistor conduction interval will 
depend on the voltages existing on the busses 478 and 480 a relatively 
large value of V.sub.CC from the collector supply bus 476 is desirable and 
a correspondingly large input signal capability for the NOR gates 412-416 
is desirable. As indicated at 458, the FIG. 4 apparatus contemplates the 
presence of additional circuits of the type shown, sixty such circuits are 
required in the preferred embodiment apparatus. 
Another voltage discriminating circuit which avoids the above-described bus 
signal variations at the input of the NOR gates in FIG. 4 is shown in FIG. 
3 of the drawings. The FIG. 3 circuit involves the use of 
operational-amplifier voltage-discriminating circuits of the type commonly 
available in integrated circuit form in the electronic art. The FIG. 3 
circuit is based on sensing the transition of the buffered V.sub.1 or 
V.sub.JS signals applied at bus 344, from a condition smaller than a 
reference signal V.sub.R, to a condition larger than the reference signal 
V.sub.R. The buffered V.sub.R reference signal is received on the bus 346 
and is appropriately divided for each of the operational amplifiers 
300-304 by the voltage dividers 336, 338 and 316, 318. The output of the 
operational amplifier 300 will, for example, approach the voltage of the 
positive supply rail for the amplifier (which is not shown in FIG. 3) so 
long as the signal at its negative input terminal is more negative than 
the signal at the positive input terminal. Once the V.sub.1 signal 
increases in magnitude and becomes more positive than the V.sub.R signal, 
the output of the operational amplifier 300 will approach the negative 
supply rail, causing conduction in the diode 328 and the resistor 330 and 
illumination of the LEDs 332 and 334. 
The reference signal on the bus 346 is shown to have a negative polarity in 
FIG. 3 in order to accommodate the polarity reversal occurring at the 
negative input of the operational amplifier 300. The use of such negative 
signals and negative or inverting amplifier input terminals and the 
corresponding polarity of the diodes 328, 332 and 334 is well known in the 
electronic art. The value of the reference signal applied to the positive 
terminal of the operational amplifier 300 and 302 is selected by adjusting 
the potentiometers 318 and 338, a precisely determined and slightly 
different value being contemplated for each of the 60 operational 
amplifiers in the preferred embodiment apparatus. 
As the V.sub.1 or V.sub.JS input signal on the bus 344 progresses in a more 
positive direction, successive ones of the operational amplifiers 300, 302 
and 304 will be turned on, that is, will switch from the positive output 
to the negative output condition. The turning on of the amplifier 302 
causes turn-off of the amplifier 300 by way of signal transmitted along 
the path 331 which adjusts the value of the reference signal supplied to 
the amplifier 300 by way of the gating diodes 342 and 340. The effective 
reference signal at each operational amplifier is the more negative of the 
signals received by way of the diodes 342, 343, and 340. In similar 
fashion, turn-on of the amplifier 304 accomplishes turn-off of amplifier 
302 and maintenance of the turn-off condition in the amplifier 300 by way 
of signal coupled along the paths 307 and 309 and the diodes 322 and 343. 
The relative values of the resistors 316 and 318, 336 and 338 determines 
the initial turn-on point for each of the operational amplifiers 300 and 
302. 
The operating band or sensitivity of each of the operational amplifiers 
300-304 in FIG. 3, that is, the band of input voltage values wherein the 
LEDs 308 and 310, for example, will remain in the energized condition can 
be adjusted with the negative feedback gain controlling resistor network 
324 and 326 in a manner known in the operational amplifier art. The use of 
such gain determining resistor elements may not be necessary, depending on 
the parameters of an individual embodiment of the circuit; this is 
indicated by omission of gain determining resistors for the operational 
amplifier 300 and inclusion of resistor 348 and 350 for the operational 
amplifier 304. 
As was indicated in FIG. 4, either a series or parallel connection of the 
symmetrically located LED elements is feasible and is indicated by the 
series connection of LEDs 332 and 334 and parallel connection of the LEDs 
308 and 310. Current limiting in each of these connection arrangements is 
provided by the resistors 312, 314 and 330. The diodes 306 and 328 serve 
to protect the LEDs from the large voltage present at the output of the 
operational amplifiers when these amplifiers are in the off state. 
It should be understood that the system herein disclosed can be arranged to 
include a plurality of the light bar and joystick elements in separate 
locations in order to provide an off-line test subject training facility 
wherein the test subjects can be acclimated to the performance of the 
system and the stress phase tasks required of them. Off-line training of 
this type can also be advantageous in avoiding the errors which tend to 
occur when learning is accomplished in the stress phase of an experiment. 
In a parallel training arrangement it would of course be possible to 
operate several of the FIG. 1 and FIG. 2 light bar array assemblies from a 
single random signal source 222 merely by paralleling driver circuits 
which are exicted by a single random signal source and also including 
plural white light elements operated from the battery 232 or an 
alternating current transformer or other energy source. The visual 
stimulus patterns in parallel operated display arrays would of course be 
identical. Such identical stimulus displays could also be used for 
competitive endeavors involved in a test subject training program. 
Off-line preliminary exposure could also be used for establishing a normal 
response time profile for test subjects outside the G force environment. 
The path 229 in FIG. 2 provides the signal needed for an off-line training 
facility. 
Both the training capability and the centrifuge mounted light bar apparatus 
may also be useful in tests involving non-human participants such as 
primate, canine, or possibly rodent test subjects--after a sufficient 
degree of training. The pursuit display of the present invention is 
believed to be more comprehendable by such a non-human subject than would 
be the compensatory display used in the prior art. The relatively low cost 
of the entire tracking acceleration tolerance tester and especially of 
off-line training stations justifies the use of multiple stations. 
Concerning the selection of visual stimulus element colors, red and green 
are standard colors for LEDs and therefore are readily available for use 
in the FIG. 1 and 2 apparatus. Studies have shown, however, that in the 
periphery of the eye, where the retinal rods rather than the cones are the 
predominant visual receptor, short wavelength light (blue, green) are more 
sensitively perceived as compared to long wavelength light (red) under G 
stress. It is therefore possible that green or white light is to be 
preferred for peripheral viewing, and that red light is less desirable in 
this use. In the present invention visual stimulus elements, however, if 
the lights were made to be all the same color, such as all green or all 
white, then the test subject could confuse the target signal with the 
response signal and have a tendency to make joystick movement in the wrong 
direction (i.e., control reversal could occur). The preferred use of LED 
visual stimulus elements of red and green colors is therefore a practical 
and desirable compromise and is not a limitation of the invention; other 
colors and other forms of stimulus elements are easily arranged. 
In the described embodiment of the invention the test subject's joystick 
104 and 242 in FIGS. 1 and 2 provide actual position control of the 
illuminated red LED array element, that is, the illuminated LED element is 
directly responsive to the position of the joystick. An alternate 
embodiment of the invention could be achieved by arranging the joystick to 
provide position incrementing of the illuminated red LED array element 
rather than actual position control. In such an embodiment the test 
subject would maintain the joystick in a neutral or home position so long 
as the illuminated red and green LEDs are aligned and move the joystick in 
an appropriate direction when alignment correction is needed. An 
embodiment of this type would, of course, somewhat approach the concept of 
the compensatory system but would retain the pursuit characteristic of the 
display. Position incrementing may be achieved using some form of 
electronic memory such as a position voltage stored on a capacitor; such a 
circuit may be fabricated using an operational amplifier connected into an 
integrating configuration with the required capacitor connected between 
the output and negative input amplifier terminals. 
It should be realized that other pattern arrangements may be employed with 
the invention, for example, a pattern wherein the array elements operate 
in thermometer fashion, e.g., commencing at the outer periphery and 
remaining in the on condition once excited up to a transition point which 
moves about randomly. Other excitation patterns involving a greater number 
of LED elements excited at a given time may also be employed. 
The described apparatus provides several notable advantages over prior art 
sensing arrangements for use with G force testing, these include the 
reduction or elimination of the tendency for test subjects to enhance or 
bravado their performance in a G stress environment, improved feedback 
psychology to the test subject through the use of pursuit display double 
arrays of visual stimulus elements, reliable operation with low 
fabrication and operating costs, a selection of visual stimulus colors 
which can be used to avoid the retina bleaching or local adaptation 
described in the above referenced prior art, and the reduction or 
elimination of test subject prediction of light patterns. 
While the apparatus and method herein described constitute a preferred 
embodiment of the invention, it is to be understood that the invention is 
not limited to this precise form of apparatus or method, and that changes 
may be made therein without departing from the scope of the invention, 
which is defined in the appended claims. 
______________________________________ 
SUM OF SINES COMPUTER PROGRAM 
______________________________________ 
PROGRAM MAIN (INPUT, OUTPUT, TAPE6=INPUT, 
TAPES5=OUTPUT) 
DIMENSION A(5,101), PHI(5), W(5), B(5), TIME(101) 
ATOTAL(102) 
C SET INITIAL CONDITIONS ON EACH SINE WAVE 
D.0. 1 I=1,5 
1 PHI(I)=RAND(I) 
C RAND(I) IS THE SUBROUTINE FOR GENERATING 
RANDOM NUMBERS 
C NOW SET THE FIVE FREQUENCIES 
WZ=2.357 
W(1)=2*WZ 
W(2)=3.*WZ 
W(3)=5.*WZ 
W(4)=7.*WZ 
W(5)=11.*WZ 
C NOW SET THE MAGNITUDES (AMPLITUDES) OF 
EACH SINE WAVE 
B(1)=1.1 
B(2)=.8 
B(3)=.6 
B(4)=.4 
B(5)=.3 
C NOW STORE THE TIME FUNCTION 
TF=5.0 
D.0. 2 I=1, 101 
2 TIME(I)=(I=1)*TF/100. 
C NOW GENERATE THE SINE WAVE 
ATOTAL(1)=0. 
D.0. 3 J=1, 101 
D.0. 4 I=1, 5 
A(I,J)=B(I)*SIN(W(I)*TIME(J)+PHI(I)) 
4 ATOTAL(J)=ATOTAL(J)+A(I,J) 
IF (I=5) 7, 7, 6 
7 ATOTAL (J+1)=0 
6 CONTINUE 
3 CONTINUE 
END 
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