Effect of Time-Sharing on Monitoring Performance: Simple Mental Arithmetic as a Loading Task

Abstract

A three-group experiment was performed to evaluate the effect of a secondary task of simple mental arithmetic on visual monitoring performance. The primary task was detection of a slightly larger excursion of a voltmeter needle making 50 uniform excursions per minute. The length of the vigil was 48 min., during which 32 signals were presented. The time-sharing group (T) performed, in addition to the monitoring task, a secondary task of adding two one-digit numbers presented auditorally 3 times a minute. Two control groups, one with the numbers presented (N) and one with only random noise (C), performed only the monitoring task. Results showed no difference in detection rate between groups, but a significant time decrement ( p < .001) and no group-by-time periods interaction. Commissive errors were significantly higher in the time-sharing group than the control groups. The results are seen as contrary to the arousal theory of vigilance.