Memory‐related eye movements challenge behavioral measures of pattern completion and pattern separation

Abstract

The hippocampus creates distinct episodes from highly similar events through a process called pattern separation and can retrieve memories from partial or degraded cues through a process called pattern completion. These processes have been studied in humans using tasks where participants must distinguish studied items from perceptually similar lure items. False alarms to lures (incorrectly reporting a perceptually similar item as previously studied) are thought to reflect pattern completion, a retrieval-based process. However, false alarms to lures could also result from insufficient encoding of studied items, leading to impoverished memory of item details and a failure to correctly reject lures. The current study investigated the source of lure false alarms by comparing eye movements during the initial presentation of items to eye movements made during the later presentation of item repetitions and similar lures in order to assess mnemonic processing at encoding and retrieval, respectively. Relative to other response types, lure false alarms were associated with fewer fixations to the initially studied items, suggesting that false alarms result from impoverished encoding. Additionally, lure correct rejections and lure false alarms garnered more fixations than hits, denoting additional retrieval-related processing. The results suggest that measures of pattern separation and completion in behavioral paradigms are not process-pure.

Time manages interference in visual short-term memory

“…The problem, in other words, may have been one of memory consolidation (Wixted, 2004). Such a conclusion is fully in line with the recent observation by Molitor et al (2014), using an eye-tracking measure to assess false alarms in a continuous recognition task like that used here: apparently errors in the task of reporting 'old' to similar items were associated with decreased fixations during the earlier presentations of those items. In a temporally densely packed sequence of items, the problem presumably was one of insufficient encoding of images into memory.…”

“…Yet Yeung et al found that mean eye fixations in their older adults did not differ across old repeated items and items sharing high similarity; apparently new items TIME MANAGES INTERFERENCE 6 were falsely viewed as old. This may have reflected either impoverished encoding in the study phase (Molitor, Ko, Hussey & Ally, 2014) or failure to identify novel visual features.…”

The Human Dentate Gyrus Plays a Necessary Role in Discriminating New Memories

“…The current lesion data might also inform the debate on process interplay, and may be applied to the question of whether pattern separation and pattern completion are two sides of the same coin or opposite ends of a continuum (Hunsaker & Kesner, 2013;Molitor, Ko, Hussey, & Ally, 2014;Vieweg et al, 2015;Yassa et al, 2011). A key element of this debate -as with other topics in cognitive neuroscience -concerns the process purity of the behavioral paradigms used to assess these cognitive operations (e.g., Molitor et al, 2014).…”

“…A key element of this debate -as with other topics in cognitive neuroscience -concerns the process purity of the behavioral paradigms used to assess these cognitive operations (e.g., Molitor et al, 2014). In the current study, even though it is assumed that the MST and MIC approximate pattern separation and pattern completion, respectively, there are other neural computations, both upstream and downstream from the dentate gyrus, which can help differentiate new information from preexisting memory traces (Deuker et al, 2014;Leutgeb et al, 2007;Myers, & Scharfman, 2011).…”

A signal detection theory analysis of behavioral pattern separation paradigms

“…Simply put: increased behavioral pattern separation should shift only the lure distribution. As mentioned above regarding dualprocess theories of memory recognition, a broader consideration when using these paradigms, however, is that there may be multiple processes contributing to the behavior (Molitor et al 2014). Therefore, behavioral paradigms alone cannot usually suffice for conclusions about neural processes (Santoro 2013), but a better behavioral measure can help to test whether there is indeed a relationship.…”