Microsaccades reveal the temporal dynamics of template and response preparation during visual search.

Abstract

Theories of visual search assume that selection is driven by an active template representation of the target object. Earlier studies suggest that template activation occurs prior to search, before the matching input appears in view, but the temporal dynamics of such pre-activation remain unclear. We demonstrate that microsaccades reflect the preparation process for visual search, in terms of both template-specific activation of target features (what to search for) and general preparation to respond (when to start searching). Participants memorized a target color (i.e. the template) for an upcoming search task. During the delay, we presented an irrelevant Rapid Serial Visual Presentation (RSVP) of lateralized colored disks and manipulated the length of the delay in blocks of long (4650 ms) and short (2790 ms) trials. Crucially, at different time points into the delay, the template color was inserted in the RSVP, allowing us to measure specific attentional biases towards this template location as a function of time. Results revealed a general suppression of saccade production in preparation to search: the closer in time to the task, the fewer saccades the participants made. Strikingly, this suppression was stronger when a template-matching disk was present. Moreover, in the time points where a template-matching disk was presented, relatively more and larger saccades went to the matching disk than to an irrelevant color, an effect that also became stronger near the end of the delay. We conclude that observers adapt search template activation to the anticipated moment of search, and that microsaccades track the dynamics of preparing for selection in visual search tasks. Meeting abstract presented at VSS 2018