The pupil old/new effect in veridical and false recognition memory

Abstract

Research has identified a pupil old/new effect: Our pupils dilate to a greater extent when we are presented with previously studied (old) items, as compared with new items. It is not yet clear what specific memory processes give rise to this effect. Using the remember–know procedure, we found that the effect was greater for items that were consciously recollected, as opposed to those that were known. We replicated the effect for auditory stimuli, ruling out any explanation of the effect based purely on visual processing. In addition, the pupil old/new effect was greatest for items that were initially encoded with a semantic orienting instruction, as compared with those encoded with a more surface orienting instruction. Using a modified Deese/Roediger–McDermott task, pupil size also increased when participants made false old responses. We conclude that the pupil old/new effect reflects a combined strength of memory signal.