title: The pupillary response discriminates between subjective and objective familiarity and novelty.
abstract: The pupil response discriminates between old and new stimuli, with old stimuli characterized by larger pupil dilation patterns than new stimuli. We sought to explore the cause of the pupil old/new effect and discount the effect of targetness, effort, recollection retrieval, and complexity of the recognition decision. Two experiments are reported in which the pupil response and the eye fixation patterns were measured, while participants identified novel and familiar object stimuli, in two separate tasks, emphasizing either novelty or familiarity detection. In Experiment 1, familiarity and novelty decisions were taken using a rating scale, while in Experiment 2 a simpler yes/no decision was used. In both experiments, we found that detection of target familiar stimuli resulted in greater pupil dilation than the detection of target novel stimuli, while the duration of the first fixation discriminated between familiar and novel stimuli as early as within 320 ms after stimulus onset. Importantly, the pupil response distinguished between the objective (during an earlier temporal component) and the subjective (during a later temporal component) status of the stimulus for misses and false alarms. In the light of previous findings, we suggest that the pupil and fixation old/new effects reflect the distinct neural and cognitive mechanisms involved in the familiarity and novelty decisions. The findings also have important implications for the use of pupil dilation and eye movement patterns to explore explicit and implicit memory processes.
authors.affiliation: School of Psychological Sciences, University of Manchester, Manchester, UK.
authors.forename: Alexandros
authors.initials: A
authors.lastname: Kafkas
authors.affiliation: School of Psychological Sciences, University of Manchester, Manchester, UK.
authors.forename: Daniela
authors.initials: D
authors.lastname: Montaldi
mesh_terms: D000293:Adolescent; D001931:Brain Mapping; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D011680:Pupil / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D021641:Recognition, Psychology / Q000502:physiology*; D055815:Young Adult
keywords: Familiarity; Novelty; Pupil old/new effect; Pupil response; Recognition memory