The Performance Assurance Computerized Test was created as a probe of two specific resources - spatial and verbal. These were selected because they reside in two anatomically separate areas of the brain. In addition, the PACT examines the critical factor of attention allocation by imposing a rapid and sustained switching between the two tasks. This combination can be regarded as an "attention stress-tolerance test" that helps to determine the brain's reserve capacity to attend. This is not unlike the strategy used by cardiovascular physiologists when imposing a heavier-than-usual load on the heart during treadmill exercise to uncover cardiac functional deficits.

A thorough validation of the PACT was undertaken by the test developers and other scientists in academia (University of California at Irvine, Harvard University's Institute for Circadian Physiology, The Systems Research Laborarory (SRL) of Dayton, Ohio, The Portuguese Air Force Center for Human Performance, The Case Western Reserve University (Cleveland), and others.

Construct-related Validity

Construct-related validity of a test is the extent to which the test may be said to measure a theoretical construct or trait. In the case of the PACT, this construct is the attention allocation function. Since the construct cannot be measured directly, construct-related validation requires the gradual accumulation of information from a variety of sources. Any data illuminating the nature of the trait under consideration and the conditions affecting its development and manifestations represent appropriate evidence for this validation (Anastasi, 1982).

Reliability

Reliability refers to the consistency of scores obtained by the same persons when reexamined with the same test on different occasions. Reliability measures allow the prediction of the range of fluctuations likely to occur in a single individual's score as a result of irrelevant, chance factors, including those which may result in part from uncontrolled testing conditions, including extreme changes in weather, sudden noises and other distractions. These are to be distinguished from variations in the test takers themselves, as illustrated by illness, fatigue, emotional strain, and worry.

Criterion-related validation procedures indicate the effectiveness of a test in predicting an individual's performance in specified activities. For this purpose, performance on the test is compared to a criterion, i.e. a direct and independent measure of that which the test is designed to predict (Anastasi, 1982).

Finally, operational feasibility studies examine the extent to which the test training, hardware, software, procedures, and so on, lend themselves to the smooth operation of a process.

A PET study, conducted at U. C. Irvine, was designed to determine the relationship between brain function (measured by glucose metabolic rate assessed with positron-emission tomography) and alcohol-related changes in performance on the PACT. Results demonstrated statistically significant correlation between alcohol-induced performance changes on the PACT and glucose metabolic rate in the parietal lobes of the brain, which have been shown to be important in maintaining attention. These correlations between brain metabolic activity and PACT performance suggest that test performance is related to the ability to maintain attention.

Thirty-two normal healthy male volunteers, age 21-35, were studied in a double-blind placebo controlled alcohol trial where subjects received sufficient alcohol to achieve a blood alcohol concentration (BAC) of 0.07 mg. % after about 30 minutes. Blood level was measured with a breathalyzer at 15-minute intervals following dosing. A subgroup of eight subjects also underwent standard cerebral glucose metabolic determinations using P.E.T. following PACT testing on both the alcohol and the placebo days.

Several of the PACT variables were statistically correlated with the alcohol-induced changes in parietal lobe glucose metabolic rate (Posner reaction time, Manikin reaction time, Manikin percent correct, transition to Manikin reaction time, Manikin percent correct, transition to Manikin reaction time, and transition to Manikin percent correct).

A Longitudinal Psychometric Study [LPS] (44; 2695) was conducted by Systems Research Laboratories, Dayton OH. Forty-four (44) Subjects (students, housewives, and truck drivers) were asked to test daily. Many subjects tested over 30 days; collectively they accomplished 2695 tests.

The ARCO Plaza Research Phase III [AP-III] (16; 254) was conducted by the ARCO Corporate Medical Department. Sixteen building security officers volunteered for daily testing lasting 30 days, completing 254 tests. (Note: ARCO is a major oil company based in Los Angeles)

The Truck Driver Study I [Vinvale] (10; 295) was conducted by The ARCO Corporate Medical Department. Ten ARCO tanker truck drivers tested daily for 30 days and a total of 295 times.

A study, conducted by the Institute for Circadian Physiology of Harvard University, demonstrated that fatigue (both between days, due to sleep deprivation, and within days over an eight hour work shift) was associated with changes in PACT performance.

The Los Angeles Sheriff's Department (LASD) Special Enforcement Bureau Study [SEB] (19; 682) was conducted by The ARCO Corporate Medical Department. Nineteen members of the S.W.A.T. team and administration, tested three times daily (pre-exercise, post-exercise, and post-shift) for 30 days, for a total of 682 tests.

Brainstem auditory evoked potentials (BAEP) in military pilots had shown effects related to amount of logged flight time. It was thought, therefore, that "aviation fatigue" may also include changes in cognition. P-300 parameters and performance on PACT were measured in three groups of military pilots differing on their average logged flight time. P-300 latency and PACT performance were found to be related to flying experience and to each other (r=.36). These data suggest that the occupation of flying military aircraft is related to the appearance of cognitive changes, which increase in severity with logged flight time.

Sixty military pilots in the Portuguese Air Force were categorized into three groups of 20 men each, based upon their logged flight time. Individuals in Group A flew less than 500 hours. Group B logged more than 500 but less than 2000 hours, and men in Group C flew more than 2000 hours. Subjects were trained on PACT and practiced until performance had stabilized. P-300s and PACT performance were subsequently measured in quiet laboratory conditions.

Criterion-Related Validity

The Vibroacoustic Syndrome (VAS) has been defined as a clinical complex suggestive of a vascular dementia. The disease appears to be caused by long occupational exposure to high levels of noise and vibration. Other disturbances which may be present include auditory and/or visual disturbances, vertigo, seizures, neurological pathological signs, and cerebrovascular disease. All affected individuals exhibit increased pericardial and mitral thickness in echocardiogram.

PACT and auditory P-300 Event-Related Potentials (ERP) were used to compare the cognitive abilities of 20 men with diagnosed VAS (the "study group") and 20 age matched men without disease, who had no occupational history of noise or vibration exposure ("control group"). Subjects received identical PACT instruction and practiced the test until their performance had stabilized. Under quiet laboratory conditions, their auditory P-300s were measured and they were tested with PACT. Results indicated: 1) P-300 latencies were significantly slower among the study group than the control group, 2) PACT Manikin Thruput was significantly slower among the study group than among the control group, and 3) there was a significant correlation between Manikin Thruput and P-300 latency (r=.32). These findings indicate that there are apparent cognitive deficits among men with diagnosed VAS, PACT performance correlates with P-300 latency (a measure considered to be closely associated with attention), and PACT may be a useful screening tool for the detection of (attention related) cognitive impairment.

Factor Analysis Study

The major purpose of the Factor Analysis study was to precisely describe the performance domain which is tapped by the PACT. PACT was presented along with a battery of other tests of information processing and attention abilities. The tests were chosen to elucidate the processing domain which is and is not tapped by the PACT. The test battery consisted of 13 tasks and measured memory capacity, spatial rotation speed, object discrimination, pattern production, and attention allocation.

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