Expansion and Contraction Modulate Visual Short-Term Memory

We examined the influence of expansion and contraction on visual short-term memory (VSTM) using a change-detection task. In each trial, several expanding/contracting line segments with various orientations were presented in two successive displays. The orientation of objects in the second display was either identical to, or different from, that of the first display. Observers were asked to judge the presence or absence of an orientation change in successive displays. Results showed that memory performance for expanding objects was higher than for contracting objects (expansion benefit: Experiments 1A and 1B). Further experiments focused on VSTM processing (encoding, storage, and retrieval). Regarding the retrieval stage, an expansion benefit was replicated only when the direction of motion was consistent between two successive displays (Experiment 2A). A cueing stimulus enhanced the memory performance for both expanding and contracting motions and eliminated the expansion benefit (Experiment 2B). Regarding the storage stage, we found the expansion benefit occurred only for shorter blank intervals between the two displays (Experiment 3). Regarding the encoding stage, the expansion benefit was observed regardless of presentation times (Experiment 4). These results indicate the possibility that expanding and contracting motions modulate VSTM.