Experience-Dependent Eye Movements, Awareness, and Hippocampus-Dependent Memory Christine N. Smith, Ramona O. Hopkins, and Larry R. Squire The Journal of Neuroscience Volume 26, Issue 44, November 1, Pages

Purpose:  What kind of memory is operating when eye movements change as a result of experience?

Background:  Memory is composed of distinct abilities that depend on different brain systems  Eye movements are signs of behavior that are measured and correlate with different types of memory  Declarative vs. Implicit memory

3 Experiments To Test:  1. If eye movements are influenced (changed) by experience memory  2. If eye movements reflect either conscious or unconscious awareness  3. If this type of identified memory and awareness is hippocampus dependent (relies on this brain system)

Design:  Participants viewed scenes that were either: novel, repeated, or manipulated  3 blocks (each with 24 images, 5s/image)  memory test for awareness  E1 & E2: measured eye movements  fixations & scanning of critical regions  E3: tested amnesic patients ability to correctly identify novel, repeated or manipulated images  measured confidence rating

Subjects  E1: 20 undergraduates; 16F, 4M  E2: 20 undergraduates; 8F, 12M  E3: 5 memory impaired patients; 4M, 1F (bilateral lesions to the hippocampus) & 10 volunteers (controls); 7M, 4F

Materials:  Binocular Apparatus: Head-rest viewpoint eye tracker (30hz) & PC-60 software (that detects pupillary position, measured fixations)  Fixations: scored as >100ms elapsed without a saccade (eye movement of within 33ms)  Position was measured by a 4X4 grid that was superimposed on image following the experiment

Results:  Eye movements did differ depending on past viewing of scenes in E1 & E2, specifically simple repetitions of an image are sufficient to change behavior  Findings were similar in E1 and E2, despite the differences in when awareness was assessed  Impaired performance on memory task & a decrease in confidence in responses of memory impaired patients in E3

E1: block 2

E1: block 3

E2: yielded similar results to E1

E3: Performance of memory impaired patients

Conclusions:  Eye movements change as a function of experience  Eye movements could not reveal unconscious forms of memory, thus eye movements reflected conscious declarative memory for what scenes were novel & repeated, and manipulated  Ability to classify images correctly & confidently relies on hippocampus-dependent, declarative memory

Bottom Line:  Experience-dependent eye movements in response to altered scenes reflect conscious, declarative memory that supports the link between:  Aware (conscious) Memory  Declarative Memory &  Hippocampus-dependent Memory