The Performance Assurance Computerized Test was created as a method to assure safety by establishing the basis for fitness rather than to try determine the causes of unfitness for duty. The PACT is predicated on a simple test of attention intended to reduce the risk of accidents in safety-sensitive jobs.

PACT was created as a probe of two specific resources - spatial and verbal. These were selected because our cognitive ability to process themoriginates 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-test”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.