U.S. patent application number 11/881175 was filed with the patent office on 2009-01-08 for method for measuring visual function and visual attention in a continuous performance test.
This patent application is currently assigned to ComputerPsych LLC.. Invention is credited to Michael E. Legatt.
Application Number | 20090009718 11/881175 |
Document ID | / |
Family ID | 40221137 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090009718 |
Kind Code |
A1 |
Legatt; Michael E. |
January 8, 2009 |
Method for measuring visual function and visual attention in a
continuous performance test
Abstract
The invention comprises a neuropsychological test method
designed to measure a test subject's variables of visual attention
for stimuli believed to preferentially elicit specific visual
pathways. Target visual pathways include the magnocellular on/off,
parvocellular chromatic red/green, koniocellular blue/yellow, and
parvocellular achromatic pathways. Furthermore, the invention
computes differential measures between the different stimuli types
for diagnostic value. These computations include, but are not
limited to, measures believed to elicit non-linear contrast gain
control, on versus off pathways, and changes in performance over
time. The test displays both target and noise (non-target) stimuli
with different apriori probabilities at different stages of the
test. The test can capture and analyze physiological measures,
isoluminant points and critical flicker fusion points. In
accordance with the present invention, a novel method and system
called the "Variable Contrast Continuous Performance Test (VC-CPT)"
is provided.
Inventors: |
Legatt; Michael E.; (Austin,
TX) |
Correspondence
Address: |
Robert S. Stoll
4710 Empire State Building
New York
NY
10118
US
|
Assignee: |
ComputerPsych LLC.
|
Family ID: |
40221137 |
Appl. No.: |
11/881175 |
Filed: |
July 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60834502 |
Jul 31, 2006 |
|
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Current U.S.
Class: |
351/246 |
Current CPC
Class: |
A61B 3/032 20130101;
A61B 5/022 20130101; A61B 5/024 20130101; A61B 5/16 20130101 |
Class at
Publication: |
351/246 |
International
Class: |
A61B 3/18 20060101
A61B003/18 |
Claims
1. A method for administering a test regime to simultaneously
measure visual function and visual attention, comprising: a.
applying stimuli believed to preferentially elicit specific visual
pathways to a subject, b. measuring the subject's responses to said
stimuli, and c. analyzing said responses by computer program means
to measure visual function and visual attention.
2. A method for administering a test regime to measure visual
attention and function in accordance with claim 1, wherein
performance to stimuli groups are contrasted in order to assess: a.
measures of visual attention, and b. measures of visual system
function.
3. A method for administering a test regime to measure visual
attention and function in accordance with claim 1, wherein
measuring the responses comprises: a. electronically recording the
critical flicker fusion point during the test, b. electronically
recording galvanic skin response during the test, c. electronically
recording heart rate during the test, d. electronically recording
blood pressure during the test, e. electronically recording eye
movement during the test, f. electronically recording pupil
dilation during the test, g. electronically recording other
biophysical or other measurements, and h. communicating said
recordings to said computer program means.
4. A method for administering a test regime to measure visual
attention and function in accordance with claim 1, wherein
participant responding can communicated to computer program means
via: a. variable responding (e.g., degree to which a lever is
pressed), b. binary responding (e.g., whether a mouse button is
pressed), c. button-up responding (releasing a pressed button
indicates a response), d. button-down responding (pressing a
released button indicates a response), and e. measurement of a
response conclusion (e.g., pressing a button back down in a
button-up paradigm).
5. A method for administering a test regime to measure visual
attention and function in accordance with claim 1, wherein test
stimuli are generated to: a. specific luminance and contrast
levels, rather than pixel gray levels, and b. if necessary,
comprised of multiple luminance levels in order to achieve a
desired overall luminance.
6. A method for administering a test regime to measure visual
attention and function in accordance with claim 1, wherein
analyzing said responses by computer program means comprises: a.
computing raw response variables, b. computing timing-based
variables, c. computing detection theory variables, d. each of said
variables being computed for each individual pathway, e. each of
said variables being computed for ranges of time, and f. each of
said variables being computed for each a priori probability.
7. A method for administering a test regime to measure visual
attention and function in accordance with claim 6, wherein said
individual pathways that are preferentially elicited include: a.
magnocellular on, b. magnocellular off, c. parvocellular achromatic
on, d. parvocellular achromatic off, e. parvocellular chromatic
red, f. parvocellular chromatic green, g. koniocellular blue, h.
koniocellular yellow, i. non-linear contrast gain controlled
aggregate on, and j. non-linear contrast gain controlled aggregate
off.
Description
REFERENCE TO RELATED APPLICATION
[0001] Reference is made to provisional patent application
60/834,502, filed Jul. 31, 2006, to which claim of priority is
hereby made pursuant to 35 U.S.C. 120.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates to the field of computer-based
testing and neuropsychological/neuroscientific testing.
BACKGROUND OF THE INVENTION
[0003] In 1956, Rosvold, Mirsky, Sarason, Bransom and Beck,
developed the first continuous performance test (CPT), a task of
visual attention that measured an individual's ability to sustain
performance over time, termed vigilance. Since that original CPT,
several variants of the test have been developed, often with good
reliability in distinguishing individuals without neurological
impairment from those with attention deficit/hyperactivity
disorder, schizophrenia, traumatic brain injury, dementia,
Parkinson's disease, and developmental dyslexia, to name a few
(Riccio, C. A., Reynolds, C. R., Lowe, P. A. (2001). Clinical
applications of continuous performance tests: Measuring attention
and impulsive responding in children and adults. New York:
Wiley).
[0004] Many continuous performance tests function through the
visual medium, displaying stimuli to which participants are
instructed to respond or ignore based on some salient features of
the stimuli. For example, in the Conners' Continuous Performance
Test (Conners, C. K. (2000). Conners' Continuous Performance Test
(CPT-II): Computer program for Windows, technical guide and
software manual. Multi-Health Systems: New York), a stimuli that
should not receive a response (noise stimuli) is a single letter
`X` on the screen, while all other single letters on the screen
should receive a response (target stimuli). Another popular CPT,
the Cornblatt Identical-Pairs CPT (Cornblatt, B. A., & Kelip,
J. G. (1994). Impaired attention genetics, and the patho-physiology
of schizophrenia. Schizophrenia Bulletin, 20 (1), 31-46) assigns
target stimuli to a number or image that repeats twice.
[0005] From the results of several trials, CPT tasks are used to
measure several components of executive function. Executive
function includes the sustaining of attention, maintaining of
response sets, set-shifting, problem solving, and planning and
following through on tasks (Cohen, R. A. (1993). Attentional
control: Subcortical and frontal lobe influences. In R. A. Cohen
(Ed.), The neuropsychology of attention (pp. 219-254). New York:
Plenum Press).
[0006] While neuropsychological models of executive function and
attention contain areas throughout the brain, the majority of the
components are contained in the frontal lobe and its projections.
Individuals with focal frontal lobe damage most often complain of
difficulties in attention and concentration (Riccio, C. A.,
Reynolds, C. R., Lowe, P. A. (2001). Clinical applications of
continuous performance tests: Measuring attention and impulsive
responding in children and adults. New York: Wiley).
[0007] Visual CPT tasks tend to rely on stimuli that, based on
current understanding of the visual system, intrinsically trigger
several visual pathways. However, deficits in a participant's
visual system would likely reduce CPT task performance, indicating
that the task is in fact not fully measuring visual attention, but
visual function as well.
[0008] For example, presume a stimulus presentation on a typical
CPT task. When a CPT stimulus spontaneously appears on the screen,
the hard boundaries between the character's edge and background and
sudden large-scale changes in luminance in the regions of the
character are likely to trigger a magnocellular response in an
individual with intact magnocellular function. The magnocellular
response is faster than the response of other cells. Therefore, on
average, an individual with deficient magnocellular function will
perceive the appearance of the character more slowly and therefore
will respond later. However, the individual's attention may still
be strong, but inaccurately measured as deficient.
[0009] Visual dysfunction is noted in many disorders.
Magnocellular-pathway deficits are noted to occur in developmental
dyslexia (Omtzigt, D., Hendriks, A. W., & Kolk, H. H. J.
(2002). Evidence for magnocellular involvement in the
identification of flanked letters. Neuropsychologia, 40,
1881-1890). NMDA-based non-linear contrast gain control (Zemon, V.,
Butler, P. D., Gordon, J., Jalbrzikowski, M., Javitt, D. C.,
Piesco, J., Russo, J., & Schechter, I. (2004). Neural
dysfunction in schizophrenia: contrast-response functions and a
nonlinear model, Program No. 347.122004 Abstract Viewer and
Itinerary Planner. Washington, D. C. Society for Neuroscience,
Online; Butler, P. D., Zemon, V., Schechter, I., Saperstein, A. M.,
Hoptman, M. J., Lim, K. O., Revheim, N., Silipo, G., & Javitt,
D. C. (2005). Early-Stage Visual Processing and Cortical
Amplification Deficits in Schizophrenia. Archives of General
Psychiatry, 62 (5), 495-504; Kwon, Y. H., Nelson, S. B., Toth, L.
J., & Sur, M. (1992). Effect of stimulus contrast and size on
NMDA receptor activity in cat lateral geniculate nucleus. Journal
of Neurophysiology, 68, 182-195) and magnocellular deficits
(Butler, P. D., Zemon, V., Schechter, I., Saperstein, A. M.,
Hoptman, M. J., Lim, K. O., Revheim, N., Silipo, G., & Javitt,
D. C. (2005). Early-Stage Visual Processing and Cortical
Amplification Deficits in Schizophrenia. Archives of General
Psychiatry, 62 (5), 495-504; Schechter, I., Butler, P. D., Silipo,
G., Zemon, V., & Javitt, D. C. (2003). Magnocellular and
parvocellular contributions to backward masking dysfunction in
schizophrenia. Schizophrenia Research, 64, 91-101) are found in
schizophrenia. Magnocellular, parvocellular, and koniocellular
deficits are found in Parkinson's disease (Silva, M. F., Faria, P.,
Regaterio, F. S., Forjaz, V., Januario, Freire, A., Castelo-Branco,
M. (2005). Independent patterns of damage within magno-, parvo- and
koniocellular pathways in Parkinson's disease. Brain, 128 (10),
2260-2271). In traumatic brain injury, magnocellular deficits are
noted in children with extremely low birth weights (Downie, A. L.,
Jakobson, L. S., Frisk, V., Ushycky, I. (2003). Periventricular
brain injury, visual motion processing, and reading and spelling
abilities in children who were extremely low birthweight. Journal
of the International Neuropsychological Society, 9 (3), 440-449),
and cortical gain control deficits are noted in adults (Du, T.,
Ciuffreda, K. J., Kapoor, N. (2005). Elevated dark adaptation
thresholds in traumatic brain injury. Brain Injury, 19 (13),
1125-1138).
[0010] Therefore, this invention was developed, based on the
current understanding of the visual system, to provide a novel
method to assess visual attention in each visual pathway
discretely. The invention aims to provide a more accurate
representation of the contributive roles of visual function and
visual attention in a participant's performance.
BRIEF SUMMARY OF THE INVENTION
[0011] In accordance with the present invention, a novel method and
system called the "Variable Contrast Continuous Performance Test
(VC-CPT)" is provided for simultaneously measuring a participant's
visual attention and visual pathway functioning in a non-invasive
neuropsychological test setting.
[0012] This system is designed to measure visual attention and
executive function. This system is unique in its ability to
administer stimuli designed to preferentially elicit each visual
pathway separately, therefore providing a far more detailed picture
into the degree of function in the visual system, separating out
deficits in the input and attentional areas. Furthermore, this
system is unique in its ability to compare and contrast function
between specific visual pathways, able to build a profile of visual
function that may further help differentiate between
conditions.
[0013] This system is non-invasive. Many approaches to measuring
visual function involve the use of visual evoked potential (VEP)
studies or magnetic resonance imaging (MRI) studies to assess
function. Other non-invasive means of measuring visual attention
and visual function (e.g., Cheng, A., Eysel, U. T., Vidyasagar, T.
R. (2004). The role of the magnocellular pathway in serial
deployment of visual attention. European Journal of Neuroscience,
20 (8), 2188-2192; Omtzigt, D., Hendriks, A. W., & Kolk, H. H.
J. (2002). Evidence for magnocellular involvement in the
identification of flanked letters. Neuropsychologia, 40, 1881-1890)
focus on a particular visual pathway (most often one of the
magnocellular pathways). By overcoming these limitations, this
system is able to offer higher accuracy in reporting visual
attention, and to better offer clinical and research utility in the
diagnosis and investigations of conditions that affect visual
attention and/or the visual system.
[0014] This invention is able to measure a participant's response
in a continuous fashion (rather than a discrete up/down fashion).
Therefore, it is able to provide measures of "near fires," in which
the participant begins to press but inhibits the response before
completion. This invention can be configured to measure response in
either a press-down or press-up fashion, which can lead to a
further differential measure and greater sense of executive
control, as the button-up paradigm tends to be more cognitively
taxing (Cornblatt, B. A., & Kelip, J. G. (1994). Impaired
attention, genetics, and the patho-physiology of schizophrenia.
Schizophrenia Bulletin, 20 (1), 31-46)
[0015] This invention is able to receive data from several
different physiological measurement devices, including, but not
limited to, galvanic skin response, heart rate, and blood pressure
devices. Therefore, this invention is able to provide a more
accurate measurement of the participant's physiological arousal,
yielding additional data as to the degree of difficulty a
participant has in completing the task.
[0016] This invention is further able to receive data from an eye
tracking system. Therefore, it is able to determine whether a
stimulus is viewed properly. It also may have utility in
determining whether ocular difficulties (such as macular
degeneration and focal brain injury) are present.
[0017] As the underlying assumptions for signal detection theory
(SDT) are not always met during a testing session, the invention
additionally computes non-linear detection theory measures
(Macmillan, N. A., Creelman, C. D. (1991). Detection theory: a
user's guide. New York: Cambridge University Press) to provide more
mathematically appropriate and accurate measures.
[0018] Because different monitors and video card combinations tend
to display the same gray levels with different luminance levels,
this invention is designed to link with a photometer to determine
the exact luminance levels that occur for each possible color value
on the screen. Therefore, the presentation of stimuli should be
nearly identical from one system to another. The instrument is
further able to present stimuli of two or more levels per check,
and therefore able to approximate a mean luminance with far greater
accuracy than uniform checks of a near value.
[0019] Due to the nature of the task, this instrument collects
measurements of critical flicker fusion and points of isoluminance
for red/green and blue/yellow.
[0020] The system uses a standard personal computer system with
attached monitor. The computer system is expected to have a video
card capable of displaying images at a high (32 and 64-bit) color
depth, high refresh rate (120 Hz or higher), and high resolution.
At present, the ability to achieve sufficient luminance brightness
and reliability is largely limited to cathode-ray tube (CRT)
displays. Depending on the intended mode of administration (binary
or continuous), either an attached mouse or custom switch is
connected as well.
[0021] The system's operation entails a test participant taking a
brief (under twenty-minute) test, during which he or she is
instructed to press or release a lever (mouse button or custom
switch) in response to the presentation of an array of squares.
Participants are instructed not to respond to an array of circles.
The invention has three different a priori probability levels (25%,
50% and 75% that a stimulus is a target), allowing for differential
measures of performance between probabilities.
[0022] Stimuli believed to preferentially elicit the magnocellular
pathway are presented with a spontaneous onset, at a low percentage
above (M.sub.ON) or below (M.sub.OFF) the background gray luminance
level. Currently, the invention has been tested with values 8% and
6%. Stimuli believed to preferentially elicit the parvocellular
chromatic pathways are presented at isoluminance, as red (PC.sub.R)
or green (PC.sub.G) stimuli against a gray background. Stimuli
believed to preferentially elicit the koniocellular pathway are
presented at isoluminance, as blue (KN.sub.B) or yellow (KN.sub.R)
stimuli against a gray background. Stimuli believed to
preferentially elicit the parvocellular achromatic-on pathway
modulate around a high positive background contrast (pedestal),
starting at background, ramping to the pedestal, and then
modulating first downward (PN.sub.DN) or upward (PN.sub.UP).
Stimuli believed to preferentially elicit the parvocellular
achromatic-off pathway modulate around a high negative background
contrast (pedestal), starting at background, ramping to the
pedestal, and then modulating first downward (PF.sub.DN) or upward
(PF.sub.UP). In order to assess the functioning of the NMDA-based
non-linear contrast gain control system, stimuli are presented with
a spontaneous onset at a high percentage (50%) above (CG.sub.ON)
and below (CG.sub.OFF) the background luminance level. See FIG. 2
for further information on these stimulus types.
[0023] Each stimulus is designed to focally target an individual
visual pathway, including the magnocellular on (M.sub.ON),
magnocellular off (M.sub.OFF), parvocellular chromatic red
(PC.sub.R), parvocellular chromatic green (PC.sub.G), koniocellular
blue (KN.sub.B), koniocellular yellow (KN.sub.Y), parvocellular
achromatic on (PN.sub.UP and PN.sub.DN), parvocellular achromatic
off (PF.sub.UP and PF.sub.DN), and non-linear contrast gain
control-modulated on (CG.sub.ON) and off (CG.sub.OFF) stimuli. See
FIG. 2 for further information on these stimuli.
[0024] Upon completion of the test session, the system computes
performance variables utilizing techniques including signal
detection theory (SDT), choice theory (CT), non-parametric
detection theory (NPDT), and response time measures. These
variables are computed for each group of stimuli individually, for
groups of stimuli, and for differentials between stimuli and
groups, for each a priori probability, and across all
probabilities.
[0025] It is believed that this method can be used to develop
ranges of performance in a normal population, as well as for
particular conditions, including, but not limited to, schizophrenia
(active, remissive, and close blood relative), ADHD, dementia,
Parkinson's disease, developmental dyslexia, and traumatic brain
injury.
BRIEF DESCRIPTION OF THE DRAWING
[0026] FIG. 1 shows two sample stimuli, a target dark stimulus, and
noise bright stimulus, along with their corresponding frequency
spectra (Fourier-transformed) below. The mean luminance of the two
images (zero-spatial frequency within the Fourier domain) are
identical, and the fundamental spatial frequencies are identical,
while the power is spread out more to the diagonals for the noise
stimuli. The area of the shapes is identical between the two
images.
[0027] FIG. 2 shows the twelve types of stimuli currently used in
the invention.
[0028] FIG. 3 shows the presentation pattern for the stimuli in the
invention. In order to address concerns that certain population are
unable to complete an entire test, the bulk of the data is computed
within the first nine blocks (equaling approximately six minutes
twelve seconds), although the whole test contains three such
groupings totaling approximately eighteen minutes, thirty-six
seconds. Underlined stimuli correspond to target stimuli, while
non-underlined stimuli correspond to noise stimuli.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The invention is a neuropsychological test method. Its
primary purpose is as a visual assessment of attentional
mechanisms, able to distinguish different patterns of attentional
performance and compare them with normative data. However, it also
has utility in measuring critical flicker fusion, and a measure of
fine motor speed.
[0030] The invention relies on a lookup table created with the
assistance of a photometer to associate the monitor's gray levels
(0-255 for 32-bit color, 0-65535 for 64-bit color) with photometric
luminance. These luminance levels are computed at least once every
three months, in order to ensure a high degree of accuracy in
stimulus generation.
[0031] Using this data (and the subject's chromatic flicker fusion
points for chromatic stimuli), the invention presents stimuli
believed to preferentially elicit each individual visual pathway,
particularly the magnocellular, parvocellular chromatic,
koniocellular, and parvocellular achromatic. In order to assess the
function of the glutamate-based non-linear contrast gain control
system, additional high luminance-contrast stimuli are
presented.
[0032] While configurable, the invention is intended for use on a
high resolution, high color depth and high refresh rate display.
The invention is capable of functioning in either a 32-bit or
64-bit color depth, and translating each gray level to an expected
luminance based on the photometric calibration. The invention is
intended to run at a high refresh rate, in order to reduce or
eliminate external flicker and have a high degree of control in
stimulus presentation. The invention has been tested at a refresh
rate of 120 Hz.
[0033] Before the test begins, participants' isoluminant points are
determined for red, green, yellow, and blue. This is achieved by
displaying an isolated checkerboard against the same background
used during the actual test. Using the up/down keys, the
participants control the depth of modulation of each of the colors,
while the frequency is set at 20 Hz. This frequency is
configurable, however, in case the participant is unable to
perceive modulation at that high a frequency. The monitor is set to
the same resolution and refresh rate as is used during the test
session.
[0034] Furthermore, critical flicker fusion is measured using a
small external device consisting of several light emitting diodes
(LEDs) and an amplifier, connected to the computer's sound card.
The sound card emits a pure tone (either sine or square wave),
which via the amplifier, drives the LEDs. The participant is asked
to several times control the frequency of the sound in order to
locate the point at which the perceived flickering appears or
disappears. After ten trials (five until the modulation disappears,
five until it appears), the average frequency is recorded. Based on
current understanding of the visual system, this frequency will
provide an additional understanding into the intactness of the
participant's magnocellular function.
[0035] After measuring the participant's isoluminant and critical
flicker fusion points, chosen physiological measurement devices are
calibrated. If galvanic skin response is included, baseline
measurements are collected at this point. Participants are
additionally offered to spend a few minutes to get used to the test
paradigm via a practice session.
[0036] Stimuli for the invention consist of a 10.times.10 isolated
checkerboard pattern centered on the screen, either consisting of
filled squares or filled circles (See FIG. 1). At the center of the
image is a fixation crosshair intended to assist the participant to
maintain visual focus, and to provide a target point for an eye
tracker in order to determine the degree of visual drifting that
occurs.
[0037] The stimuli are presented centered on the screen, against a
background of a set luminance. The stimuli are calibrated so that
each has identical height and width when displayed on the screen at
the set resolution. In the event that the intended luminance of the
squares is not equal to the luminance of a particular gray level,
pixels of the luminance levels directly above and below that point
are interspersed to create a stimulus with an average luminance
nearly identical to the intended level. This same weighted
averaging is used to produce the background at the intended
luminance. This weighted averaging helps ensure that the invention
functions well across multiple platforms and over time.
[0038] The luminance levels of the shapes and the mode of their
presentation (spontaneous, gradual or pedestal) are based on the
target visual pathway. Participants are instructed to respond to
the square stimuli (targets) and not to the circle stimuli (noise).
Depending on the mode of testing, participants respond either by
pressing down on a lever and quickly releasing it, or by releasing
a lever and quickly repressing it and holding it down until the
next target.
[0039] When analyzed in the frequency (Fourier) domain, the target
and noise stimuli have identical zero and fundamental spatial
frequencies, although the power is more spread to the diagonals for
the noise stimuli than for the target stimuli.
[0040] For the magnocellular pathway, the stimuli are presented
with a spontaneous onset, at a low percentage above (M.sub.ON) or
below (M.sub.OFF) the background gray luminance level. Currently,
the invention has been tested with values 8% and 6%. For the
parvocellular chromatic pathways, the stimuli are presented at
isoluminance, as red (PC.sub.R) or green (PC.sub.G) stimuli against
a gray background. For the koniocellular pathway, the stimuli are
presented at isoluminance, as blue (KN.sub.B) or yellow (KN.sub.R)
stimuli against a gray background. For the parvocellular achromatic
pathway, the stimuli modulate around a high background contrast
(pedestal), starting at background, ramping to a positive (PN) or
negative (PF) contrast, and then modulating first downward
(PN/PF.sub.DN) or upward (PN/PF.sub.UP). In order to assess the
functioning of the NMDA-based non-linear contrast gain control
system, stimuli are presented with a spontaneous onset at a high
percentage (50%) above (CG.sub.ON) and below (CG.sub.OFF) the
background luminance level. See FIG. 2 for further information on
these stimulus types.
[0041] While taking this test, several physiological measurements
are obtained every 0.25 seconds. Measures, as available, currently
include galvanic skin response (GSR), heart rate, blood pressure,
eye position (deviation from the fixation crosshair) and pupil
dilation. The invention can, using dynamic link libraries (DLLs),
receive configurable data either in real time or by import after a
test's completion.
[0042] The apriori probability of a stimuli being a target will
vary across the test between 25%, 50%, and 75%. See FIG. 3 for a
sample of a test pattern designed to balance stimulus types across
the testing session. While configurable, the stimulus presentation
duration defaults to 250 ms, and the time between the offset of one
stimulus and onset of the next defaults to 1, 2, and 4 seconds. An
alternate configuration supports two adjacent stimulus
presentations of a set presentation time (e.g., stimulus
presentation for 100 ms, blank for 50 ms, present again for 100
ms).
[0043] After each stimulus is presented on the screen, a response
from the participant before the presentation of the next stimulus
is noted. If a response occurs and the stimulus was a target, it is
considered a hit. If a response occurs and the stimulus is noise,
it is considered a false alarm. A non-response to noise is
considered a correct rejection, and non-response to a target is
considered a miss. In the event of a response to a stimulus, the
time between the initial onset of the stimulus and the response is
recorded (reaction time to hits, reaction time to false positives).
When the participant stops responding (by either releasing or
repressing the lever depending on the instructions), the
differential between the beginning and end of the response is
computed (reset time to hits, reset time to false positives).
[0044] If responding is measured in a continuous fashion, threshold
computations are made at liberal, average, or conservative levels
of what is considered a response based on the range of the
participant's responding. Computations of means, standard
deviations, and accelerations are presented for each
interpretation.
[0045] Upon completion of the task, the invention computes the
following variables based on the test data: [0046] 1. Raw response
variables [0047] a. Hit proportion (number of hits/number of
targets) [0048] b. False alarm proportion (number of false
alarms/number of noise) [0049] c. Correct Rejection proportion
(number of correct rejections/number of noise) [0050] d. Miss
proportion (number of misses//number of targets) [0051] e. Percent
correct ((number of hits+number of correct rejections)/number of
stimuli) [0052] f. Standard error of percent correct [0053] 2.
Timing-based variables [0054] a. Mean and standard deviation:
reaction time to hits, reaction time to false alarms [0055] b. Mean
and standard deviation time: reset time to hits, reset time to
false alarms [0056] 3. Signal detection theory (CT) variables
(Green & Swets, 1966) [0057] a. Sensitivity (d') and standard
error [0058] b. Criterion location (c) and standard error [0059] c.
Relative criterion location (c') [0060] d. Response likelihood
ratio (.beta..sub.G) [0061] 4. Choice theory (CT) variables (Luce,
1959) [0062] a. Sensitivity (.alpha.) [0063] b. Transformed
sensitivity (ln(.alpha.)) [0064] c. Bias (b) [0065] d. Transformed
bias/criterion location (ln(b)) [0066] e. Relative criterion
location (b') [0067] f. Response likelihood ratio (.beta..sub.L)
[0068] 5. Non-parametric detection theory (NPDT) variables
(Macmillan, N. A., Creelman, C. D. (1991). Detection theory: a
user's guide. New York: Cambridge University Press) [0069] a.
Sensitivity (q) [0070] b. Criterion location (k) [0071] c. Relative
criterion location (k') [0072] d. Sensitivity (A') [0073] e.
Transformed sensitivity (A'') [0074] f. Bias (B'') [0075] 6.
Physiological variables (as available)--Each value's mean, mode,
median, minimum and maximum are correlated with Raw, timing, SDT,
CT and NPDT variables. [0076] a. Galvanic Skin Response [0077] b.
Eye tracking location variables (Deviation of vertical and
horizontal offset from the fixation crosshair) [0078] c. Pupil
dilation [0079] d. Eye tracking saccade counts [0080] e. Eye
tracking loss (eye blink) counts [0081] f. Blood pressure [0082] g.
Heart rate [0083] h. Any other physiological measure that can be
reported to the invention through an external device (continuous or
discrete variables), or computed from that data.
[0084] Each of these variables is computed for each stimulus type
believed to preferentially elicit a particular visual pathway
(magnocellular on, magnocellular off, parvocellular chromatic red,
parvocellular chromatic green, koniocellular blue, koniocellular
red, parvocellular achromatic on-up, parvocellular achromatic
on-down, parvocellular achromatic off-up, parvocellular achromatic
off-down, contrast gain on, contrast gain off). Computations are
also performed for the aggregate magnocellular, parvocellular
chromatic, koniocellular and contrast gain stimuli, as well as for
all ON and all OFF stimuli. Differential measures are also computed
between each ON and OFF stimuli, between the parvocellular
achromatic UP and parvocellular achromatic DOWN stimuli, and
between each type of stimuli.
[0085] While the foregoing is illustrative of a preferred
embodiment of the invention, other embodiments and modifications
and improvements are intended to come within the scope of the
invention and of the appended claims.
* * * * *