Pupil Dilation During Recognition Reflects the Subjective Recollection/Familiarity Experience at Test Rather Than the Level of Processing at Encoding

Pupil dilation provides a window into recognition memory processes. During a recognition test, the pupil dilates more in response to a recognized studied item than to a correctly rejected new item. Various explanations for this pupil old/new effect have been offered. By a retrieval effort account, the pupil’s response on a recognition test reflects the cognitive effort needed to retrieve items from memory. By a memory strength account, pupil dilation reflects the strength of the subjective memory experience elicited by items at test. To compare these accounts, we varied levels of processing (LOP) at study, then measured pupil dilation on a delayed recognition test during which participants made recollection/familiarity judgements. Pupil dilation at test was similar whether test items had been studied in a deep or shallow LOP task, but was greater when deep, shallow, and new test items were experienced as recollected rather than as familiar. This pattern supports the memory strength account rather than the retrieval effort account of pupil dilation during a recognition test