Eye-Movement Correlates of Pattern Separation in a Mnemonic Similarity Task Modified with Naturalistic Scenes

Abstract: Pattern separation is one of the central operations of episodic memory. Tasks that evaluate the pattern separation usually base their assessments on the behavioral recall of simple objects or words and are far from real-life experiences and daily memory performance. Thus, typical tasks that assess pattern separation lack ecological validity. To address this issue, we designed a mnemonic memory test by creating naturalistic visual stimuli consisting of objects in contexts. Such stimuli are particularly beneficial for eye-tracking assessment in unrestricted viewing. Eye movements provide in-depth information about how memory is formed and retrieved compared to the usual behavioral assessment. We presented participants with images of everyday scenes while recording their eye movements, and then tested their recognition memory in a spatial discrimination test. A novel multi-dimensional scanpath similarity analysis was used to unfold the role of scanpath overlap between encoding and retrieval. We found that fixation duration and fixation number predict indexes related to pattern separation at encoding but not retrieval. Lure correct rejections had fewer fixations and higher fixation durations at retrieval compared to other combinations of conditions (lure, target) and responses (correct, incorrect). Position scanpath replay supported correct recognition. Moreover, we observed that higher perceived stress was associated with impaired lure discrimination ability and increased overgeneralization. Overall, our study showed a high sensitivity of the combination of naturalistic viewing tasks and eye tracking to memory performance, which may help assess and diagnose cognitive impairment.