The Effect of Visual Long-Term Memory on Eye Movements over Time

Visual long-term memory (VLTM) of complex visual stimuli such as photographs of scenes has previously been shown to significantly affect eye movements. This effect manifests as a decrease in saccade amplitude and increase in fixation duration as images are shown repeatedly within one experimental session. VLTM is known to have a much longer temporal persistence, however. In a series of two experiments we investigate the transfer of the effects of VLTM on eye movements to longer time scales. The first experiment was comprised three sessions spread over several days. In each session participants viewed and memorized a sequence of images. In Session 1 all presented images were unfamiliar to participants. Sessions 2 and 3 included (a) images familiar from Session 1, (b) semantically and structurally similar images, and (c) unfamiliar images. Participants showed the expected proficiency in recognizing images even days after exposure. However, using a mixed linear model approach, we found no evidence of image familiarity on eye movement measures like fixation duration and saccade amplitude. The effect on target selection, as quantified by the likelihood of fixation locations given the empirical distribution of fixation locations, was weakly significant. In a second experiment we reduced the time between sessions by conducting Session 1 and 2 on the same day, and Session 3 on the following day. As in the previous study, the results showed that the influence of VLTM on eye movements is weaker than when presentations occur within the same session. These results are compatible with the view that, while memory of an image remains intact over days, the immediate effect of VLTM on eye movement metrics decays much faster. Only hours after memorizing an image, scene exploration is primarily driven by the current visual input and independent of VLTM.