The contributions of expectancy and prior exposure to the surprise response in visual search.

In the context of visual search, surprise is the phenomenon by which a previously unseen and unexpected stimulus exogenously attracts spatial attention. Capture by such a stimulus occurs, by definition, independent of tasks goals and is thought to be dependent on the extent to which the stimulus deviates from expectations (Horstmann, 2005, JEP:HPP). However, the relative contributions of prior exposure and expectation to the surprise response have not yet been systematically investigated. Here we investigated the extent to which surprise is related to never having seen a given stimulus before (exposure hypothesis) versus the extent to which a given stimulus violates task expectancies (expectation hypothesis). In a spatial cueing paradigm, observers had to search for a specific colour while ignoring irrelevant distractors of different colours presented prior to the target display (pre-cues). After a brief familiarization period, we presented an irrelevant motion cue to elicit surprise. Across conditions we varied prior exposure to the motion stimulus – seen versus unseen - and top-down expectations of occurrence – expected versus unexpected - to assess the extent to which each of these factors contributes to surprise. We found no difference in the magnitude of the surprise response associated with a previously seen but unexpected motion cue and a previously unseen but expected motion cue. These results suggest that the expectancies driving surprise may have different characteristics than previously thought and that surprise may be immune to cognitive strategies to attenuate it. Meeting abstract presented at VSS 2013