Previously seen and expected stimuli elicit surprise in the context of visual search

Abstract

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 task goals and is thought to be dependent on the extent to which the stimulus deviates from expectations. However, the relative contributions of prior-exposure and explicit knowledge of an unexpected event to the surprise response have not yet been systematically investigated. Here observers searched for a specific color while ignoring irrelevant cues of different colors presented prior to the target display. After a brief familiarization period, we presented an irrelevant motion cue to elicit surprise. Across conditions we varied prior exposure to the motion stimulusseen 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 attenuation of the surprise response when observers were pre-exposed to the motion cue and or had explicit knowledge of its occurrence. Our results show that it is neither sufficient nor necessary that a stimulus be new and unannounced to elicit surprise and suggest that the expectations that determine the surprise response are highly context specific.Keywords Visual search . Surprise . Attentional capture There is more information present in any given visual scene than the human cognitive system is capable of fully processing at any one point in time. A challenge for the human visual system then is to construct a stable and functional percept of the world from only a select subset of the available visual input. Mechanisms of selective attention allow us to prioritize the processing of certain visual input so that our conscious percept is one constructed from information in the environment that is functionally pertinent. How these selection mechanisms are controlled and the information they are sensitive to has important consequences for how we interact with our environment. In everyday life, the visual system is frequently challenged to decide whether to attend to information that is relevant to our immediate goals or to prioritize signals that might be unexpected and signal a threat.Much of the debate in the literature over attentional control has focused on the nature of control of the exogenous attentional system -a system that reflexively shifts the focus of attention to signals of potential importance in the environment. At issue is the degree to which bottom-up factors, namely stimulus saliency, automatically capture attention and to what degree top-down, namely task goals, modulate the effect of salient stimuli (Jonides & Yantis, 1988;Lamy & Kristjánsson, 2013;Leber & Egeth, 2006;Müller, Geyer, Zehetleitner, & Krummenacher, 2009;Posner, 1980;Remington, Johnston, & Yantis, 1992;Shomstein, 2012;Theeuwes, 1991Theeuwes, , 2010Yantis & Jonides, 1984). Previous studies investigating orienting, especially in natural scenes, suggest that salience may i...