The obligatory effects of memory on eye movements.

Previous work has shown that eye movement behaviour is affected by previous experience, such that alterations in viewing patterns can be observed to previously viewed compared to novel displays. The current work addresses the extent to which such effects of memory on eye movement behaviour are obligatory; that is, we examined whether prior experience could alter subsequent eye movement behaviour under a variety of testing conditions, for stimuli that varied on the nature of the prior exposure. While task demands influenced whether viewing was predominantly directed to the novel versus familiar faces, viewing of the familiar faces was distinguished from viewing of the novel faces, regardless of whether the task required incidental encoding or intentional retrieval. Changes in scanning of previously viewed over novel faces emerged early in viewing; in particular, viewing duration of the first fixation to the familiar faces was often significantly different from the duration of the first fixation directed to the novel faces, regardless of whether prior exposure was solely in the context of the experiment or due to real-world exposure. These findings suggest that representations maintained in memory may be retrieved and compared with presented information obligatorily.