Saying "yes" when you want to say "no" - pupil dilation reflects evidence accumulation in a visual working memory...

A number of studies have shown that the pupil dilates during stimuli recognition and decision-making. Yet, little is known about the interaction between recognition memory and decision processes. Here, we investigated the possible link between pupil response and decision-related factors during a visual recognition task. Forty-eight volunteers took part in the study. The experimental task was based on the Deese-Roediger-McDermott paradigm designed to study false recognitions. Participants were shown different sets of two meaningless objects. After seeing each set, they were asked to determine whether the subsequent probe (positive, lure or negative) was already presented. We had found that the pupil dilated more and slower, and the reaction time was extended, when the upcoming choice was against individual response bias. Such a result indicates that recognition and rejection in memory tasks could be seen as two behavioral alternatives supported by evidence accumulation, in line with decision-making models. This interpretation was upheld with the drift-diffusion modelling based on pupil data. A similar pattern was observed for errors - larger pupil sizes before incorrect responses were accompanied by longer reaction times. Furthermore, before correct reactions, especially in participants differentiating more accurately between the old and new stimuli, pupil dilation was increasing faster, indicating swifter evidence accumulation. Taking into account the link between cognitive pupillary reflex and norepinephrine release, we conclude that similarly to decision making, reactions in memory tasks may partly depend on the locus coeruleus activity, which is the principal site for norepinephrine synthesis.