Pupillary responses during mental activities

Abstract

With a new electronic technique, pupil size of 40 Ss was measured continuously during a series of intellectual tasks. Time estimation or counting elicited no pupillary changes, but pupil diameter reliably increased (approximately 30%) during number memory, multiplication, and word definition. Dilation was greater for novel or more difficult tasks. If S continued to work a problem after answering, dilation persisted, but silent counting by S terminated task perseveration and dilation. Thinking about pleasant or unpleasant experiences elicited inconsistent dilation, constriction, or no change. © 1968, Psychonomic Journals. All rights reserved.