SCRI’s Tests and Equipment

Audiometer

A portable audiometer allows pure-tone threshold testing. Auditory thresholds are determined for both ears by adapting the sequence of stimulus presentation to the subject’s responses. The down two, up one rule is normally used on frequencies ranging from 250 Hz to 8000 Hz.

Bender-Gestalt

The Bender-Gestalt Test requires the subjects to copy a series of patterns printed on nine cards. Evaluation of the test depends on the relationship between the various components of each pattern.

Critical Tracking Task

As a trial on the critical tracking task begins, the video monitor displays a vertically-oriented arrow at center screen. A forcing function begins to move the arrow horizontally to the left and right of center. The subject uses a steering wheel in an effort to counteract the forcing function and keep the arrow centered.

The task becomes more and more difficult as the arrow’s instability gradually increases. Eventually, the subject cannot compensate for the forcing function. Within 60 seconds of trial initiation, he/she loses control, the trial ends, and lambda, the just-controllable difficulty level for the trial, is stored into memory. A run consists of 25 trials with the first five trials serving as warm-up. The following measures are recorded.

· Average lambda

· Standard deviation of lambda.

Divided Attention Task

The divided attention task requires the subject to simultaneously allocate attention to two different tasks, pursuit tracking and visual search. The tracking task appears on a centrally-located screen. It requires the subject to follow a red ball with a white cross. The red ball moves horizontally in response to a forcing function, and the white cross is controlled by joystick. The distance between the ball and the cross is recorded as tracking error, at a rate of 60 times per second.

The visual search task requires the subject to report the appearance of the number “2” in one of four visual quadrants at the periphery of the visual field. Each quadrant is composed of a 2 x 3 number array. The numbers change in a random manner with the constraint that a target appears twice in each of the 24 possible locations during the 12-minute trial. To report a signal, the subject presses a button on a response pad corresponding to the quadrant in which the signal appeared. Each of the 48 targets remains displayed until the subject detects it and responds to it or until 10 seconds elapse. The following measures are recorded:

· Tracking task

· Mean absolute tracking error

· Visual search

· Response latency (seconds)

· Number of correct responses

· Number of errors

· Missed signals

· False alarms

· Incorrect responses.

Driving Simulator

The driving simulator consists of a steering wheel, turn signal stalk, horn, brake, and accelerator. Three 17' monitors provide a 135-degree wide field-of-view. Drivers are required to maneuver through traffic, obey traffic signals, avoid collisions, change lanes, overtake slower vehicles, and yield to pedestrian crossings.

Scenarios can be developed to simulate most types of roadways, roadway conditions, and weather conditions. An optional secondary task can be added to increase the sensory/perceptual/cognitive load of the drive. The secondary task requires drivers to respond to stimuli on the outer edges of the field-of-view. Overall, the following measures are recorded:

· Speed of travel

· Standard deviation of Speed

· Lane deviation

· Off-road accidents

· Collisions

· Pedestrians hit

· Times over posted speed limit

· Stops at traffic lights

· Drive duration

· Reaction time (RT)

· Standard deviation of RT

· Correct responses

· Incorrect responses

· Misses.

Motor-Free Visual Perception Test

The MVPT is a test of visual perception which avoids motor involvement. Subjects are presented a stimulus and are asked to locate it among four alternatives. The only response required is that the subject point to one of the alternatives. A total of 36 stimuli are presented.

Perceptual Acuity Test

The PAT is a group test of visual perception of geometric forms and optical illusions. Subjects are presented a stimulus and are asked to identify the alternative that matches the stimulus in some chosen dimension. A total of 30 stimuli are presented.

Raven’s Standard Progressive Matrices

This computerized version of the Raven’s SPM requires the subjects to look at a pattern with a missing piece and identify which of six alternatives best completes the pattern. Subjects select the correct alternative by touching it on the screen.

The  test measures eductive ability (the ability to forge new insights, the ability to discern meaning in confusion, the ability to perceive, and the ability to identify relationships). It is believed to be a reliable index of g, the general factor of intelligence. The computer administers the test, calculates the raw score, and provides percentile ranks for a variety of norms.

UFOV

The useful field of view consists of three subtests which assess speed of visual processing under increasingly complex task demands. During the tests, the subject must detect, identify, and localize briefly presented targets. In the first subtest, the subject identifies a target presented in a centrally located fixation box that is presented for varying lengths of time. In the second subtest, the subject identifies a target, but must also localize a second target displayed in the periphery of the computer monitor. The third subtest is identical to the second, except that the second target is embedded in a noisy background.

For each subtest, the length of the stimulus presentation is automatically adjusted using an up two, down one adaptive paradigm. After two correct responses, stimulus presentation for the next item is decreased; but after a single incorrect response, stimulus presentation for the next item is increased. The following measures are recorded in all three subtests:

· Standard The number and specification of the reversal points required to determine the perceptual threshold

· The average stimulus presentation duration at which the subject can perform the task correctly 75% of the time.

Vigilance

The test of vigilance, presented with a computer adaptation of a Macworth clock, is a lengthy and monotonous task. It is intended to be an analog to monotonous, nighttime driving along a deserted roadway. The subject’s sole task is to detect and respond to an infrequent visual signal which occurs within a background of non-signal events.

The clock appears on the computer monitor as a 10.16 cm diameter circle of 24 equally-spaced small squares. A larger square moves around the clock face in discrete jumps from one position to the next at the rate of two jumps per second. A signal is when the larger square skips one of the positions. Eight skips occur in each of 10-minute blocks (N = 32) during a continuous 40-minute test. Skips are located and timed by random procedures.

A subject monitors the display for the infrequent signal and responds by keypress. The maximum allowable response time (MART) is 5 seconds. The subject receives no feedback for his/her performance. The following are recorded for each 10-minute block:

· Response latency (seconds), with and without MART

· Number of correct responses

· Number of errors

· Missed signals

· False alarms.

Visual Acuity & Contrast Sensitivity

Visual acuity, the ability to see details, is measured with the Snellen chart and two versions of the Bailey-Lovie chart, the high-contrast version and the low-contrast version (10%). Contrast sensitivity, the ability to distinguish differences in brightness, is measured with the Pelli-Robson chart and the VCTS 6500 chart. Charts are illuminated within specified luminance ranges, without glare, with lamps out of sight.

Visual Backward Masking

The visual backward masking test is presented by computer. As a trial begins, the subject views a cross in the center of the monitor. When the “Enter” key is pressed, four letters are displayed for 16 milliseconds. After the letter display, the screen is blank for an inter-stimulus interval (ISI) of variable duration. A masking stimulus, which is made up of letter fragments, then appears for approximately 500 milliseconds. Following the mask, the subject types four letters on the computer keyboard. Typing errors can be corrected, but the response is forced-choice and the computer will only accept a response as valid when four letters have been typed into the response spaces.

 Subjects’ performance on the visual backward masking test is best described within the framework of information processing theory. The 16 millisecond stimulus presentation enters the letters into sensory (iconic) memory. While the screen is blank during the ISI, a transfer to working memory begins, but the mask disrupts the sensory image and halts processing. Only those letters which were transferred from iconic memory into working memory during the ISI, before the onset of the mask, are available for recall. The number of letters recalled as a function of ISI duration provides a measure of information processing rate.

The test uses different ISI durations, which are multiples of 16 milliseconds. Test trials present the different ISI values in ascending-descending and descending-ascending blocks. The following measures are recorded:

· Standard Correct letters (typed in correct order)

· Number of errors

· Position of errors

· Recall and error rates for specific letters

· Recall and error rates by trial number.

Wechsler Adult Intelligence Scale & Wechsler Memory Scale

The WAIS is a test designed to measure intelligence. Four domains of cognitive functioning are assessed:

· Driving task

· Speed of travel

· Standard verbal comprehension

· Perceptual organization

· Working memory

· Processing speed.

The test is often used for neuropsychological evaluations across the adult lifespan. It consists of 14 subtests.

The WMS is a test designed to measure learning and memory. Immediate, delayed, and working memory are assessed in two modalities, auditory and visual, and two task formats, recall and recognition. The test is often used for neuropsychological evaluations across the adult lifespan. It consists of 16 primary and optional subtests.