The eyes know: eye movements as a veridical index of memory

In two experiments, we examined whether observers' eye movements distinguish studied faces from highly similar novel faces. Participants' eye movements were monitored while they viewed three-face displays. Target-present displays contained a studied face and two morphed faces that were visually similar to it; target-absent displays contained three morphed faces that were visually similar to a studied, but not tested, face. On each trial in a test session, participants were instructed to choose the studied face if it was present or a random face if it was not and then to indicate whether the chosen face was studied. Whereas manipulating visual similarity in target-absent displays influenced the rate of false endorsements of nonstudied items as studied, eye movements proved impervious to this manipulation. Studied faces were viewed disproportionately from 1,000 to 2,000 ms after display onset and from 1,000 to 500 ms before explicit identification. Early viewing also distinguished studied faces from faces incorrectly endorsed as studied. Our findings show that eye movements provide a relatively pure index of past experience that is uninfluenced by explicit response strategies, and suggest that eye movement measures may be of practical use in applied settings.