Pupil Old/New Effect is Modulated by Task Instruction - Evidence for an Attentional Saliency Account

Pupil dilation (PD) is more pronounced during correct recognition of previously presented target items than during correct identification of novel, previously not seen foils. We examined whether this so-called pupil old/new effect is caused by a bottom-up attentional orienting response triggered by the activated mnemonic information. Because the magnitude of the orienting response to a given stimulus is dependent on the task-relevancy of the stimulus, we tested the potential link between orienting response and the pupil old/new effect by examining whether task-relevancy affects PD during processing of previously seen items. Specifically, we presented well-learned material intermixed with novel foils and requested participants either to semantically categorize them as animate/inanimate (non-mnemonic task), or to make an old/new recognition judgement (mnemonic task). Our results show that whereas the pupil old/new effect was present in both conditions, its magnitude was larger in the mnemonic task, where mnemonic information was relevant for the task.Thus, the pupil old/new effect was sensitive to task relevancy, and this finding is in line with the notion that increased PD triggered by correct recognition is caused by an attentional orienting response towards activated mnemonic information.