The effects of list difficulty and modality of presentation on a computerized version of the Paced Serial Addition...

The Paced Serial Addition Test (PSAT) presents a series of digits at different speeds with the requirement that the two most recent numbers be added together. Although the PSAT is a relatively difficult test, its level of difficulty may be decreased by changing the number list to make the answers simpler and by presenting the digits visually rather than aurally. In view of this, the present experiment varied both task difficulty (easy vs. hard) and mode of presentation (visual vs. auditory). Task difficulty was manipulated by using two different lists composed of single digits whose answers ranged between 2 and 10 (easy) or 2 and 18 (hard). All stimuli were presented by computer which permitted measurement of response latencies, as well as correctness of responding. The results showed that mode of presentation, but not task difficulty, produced highly significant effects. Additional evidence showed that the ability to compute answers to simple addition problems must be considered as a modulator variable. However, an individual's basic arithmetic ability is not as critical as the modality in which a stimulus is presented. The lower performance associated with the auditory version (i.e., PASAT) was interpreted as an interference effect caused by both the stimulus and the response occurring in a single auditory information processing channel. This interpretation suggests that the PASAT's well documented sensitivity to traumatic brain injury (TBI) may be due, at least in part, to an increased susceptibility to interference effects rather than attributable solely to a decreased rate of information processing.