Effects of Grouping on the Pupillary Response in a Short-Term Memory Task

Subjects heard strings of nine digits for immediate recall, either at a monotone 1/sec. rate or in groups of three digits separated by pauses. Concurrent measurements of pupil size show a steady dilation in the monotone condition, and brief dilation-constriction waves during the pauses of grouped presentation. The results are consistent with hypotheses concerning rehearsal in the two modes of presentation. Pupillary dilations apparently accompany episodes of covert rehearsal.