The Hippocampus Promotes Effective Saccadic Information Gathering in Humans

Abstract

It is well established that the hippocampus is critical for memory. Recent evidence suggests that one function of hippocampal memory processing is to optimize how people actively explore the world. Here we demonstrate that the link between the hippocampus and exploration extends even to the moment-to-moment use of eye movements during visuospatial memory encoding. In Experiment 1, we examined relationships between study-phase eye movements in healthy individuals and subsequent performance on a spatial reconstruction test. In addition to quantitative measures of viewing behaviors (e.g., how many fixations or saccades were deployed during study), we used the information-theoretical measure of entropy to assess the amount of randomness or disorganization in participants' scanning behaviors. We found that the use of scanpaths during study that were lower in entropy (e.g., more organized, less random) predicted more accurate spatial reconstruction both within and between participants. Scanpath entropy was a better predictor of reconstruction accuracy than were the quantitative measures of viewing. In Experiment 2, we found that individuals with hippocampal amnesia tended to engage in viewing patterns that were higher in entropy (less organized) relative to healthy comparisons. These findings reveal a critical role of the hippocampus in guiding eye movement exploration to optimize visuospatial relational memory.

The intersection between the oculomotor and hippocampal memory systems: empirical developments and clinical implications

“…2). 80 This is consistent with the prior work in which, unlike control participants, amnesic cases failed to show entropy differences between scenes that had either been repeated in their original form or altered from prior viewing. 6 Such findings suggest that the hippocampus and the broader MTL may play a role in the moment-to-moment guidance of viewing, as lasting representations are built and used online.…”

“…Amnesic cases also showed higher entropy (less organization or predictability) in their viewing patterns compared with control participants when they were tasked with reconstructing the spatial locations that had been previously occupied by a set of objects with high feature overlap (Fig. ) . This is consistent with the prior work in which, unlike control participants, amnesic cases failed to show entropy differences between scenes that had either been repeated in their original form or altered from prior viewing .…”

“…(A) Structural images are presented for a neurologically intact control participant, and two individuals with amnesia, as outlined in Lucas et al . The etiology for amnesic case 1846 was anoxia/hypoxia that resulted in damage confined to the hippocampus bilaterally.…”

“…Moreover, the work in cases of amnesia, aging, and neurodegeneration presented here changes how the nature of hippocampal dysfunction can be conceived. Namely, hippocampal compromise may be both more pervasive than previously thought and result in deficits beyond memory, as it changes the very manner by which visual exploration occurs …”

Reconstructing relational information

“…Participants' eye movements were recorded throughout the experiment. Eye tracking data are not reported here and will be reported elsewhere (Lucas, Duff, & Cohen, ).…”