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Boris Quétard, Jean Charles Quinton, Martial Mermillod, Laura Barca, Giovanni Pezzulo, Michèle Colomb, Marie Izaute; Differential effects of visual uncertainty and contextual guidance on perceptual decisions: Evidence from eye and mouse tracking in visual search. Journal of Vision 2016;16(11):28. doi: 10.1167/16.11.28.
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Visual search can be seen as a decision-making process that aims to assess whether a target is present or absent from a scene. In this perspective, eye movements collect evidence related to target detection and verification to guide the decision. We investigated whether, in real-world scenes, target detection and verification are differentially recruited in the decision-making process in the presence of prior information (expectations about target location) and perceptual uncertainty (noise). We used a mouse-tracking methodology with which mouse trajectories unveil components of decision-making and eye-tracking measures reflect target detection and verification. Indoor scenes were presented, including a target in usual or unusual locations or no target, and were degraded with additive noise (or no noise). Participants had to respond to the target's presence or absence. Degrading the scene delayed the decision due to increased verification times and reduced mouse velocity. Targets in unusual locations delayed the decision and deviated mouse trajectories toward the target-absent response. Detection times played a major role in these effects. Thus, target detection and verification processes influence decision-making by integrating the available sources of information differently and lead to an accumulation of evidence toward both the presence of a target and its absence.
Targets placed in unusual locations led to detection time and more fixations during the detection epoch compared to targets in usual locations. In contrast to these results, noise increased verification time and fixation duration during the detection epoch.
Both targets in an unusual location and degradation with noise increased the RT. The effect of target location was mediated by detection time whereas the effect of noise was mediated by verification time, thus clearly distinguishing the influence of both on the RT.
The x-velocity began increasing before the moment of target detection and was higher for unusual target locations than for usual from 288 ms to 128 ms before target detection to 416 ms to 496 ms after target detection. The peak of the x-velocity profiles occurred 106 ms to 191 ms after the end of target verification, and their amplitude was decreased by noise. Additionally, noise increased x-velocity in the latest parts of the profile. Hence, target location influenced the early part of the response movement whereas noise influenced the late part.
Although noise had no significant influence, the AUC was higher for targets in unusual locations than for targets in usual locations. This effect was modulated by detection times: Higher detection times further increased the AUC for targets in unusual locations compared to usual locations.
The deviation from the ideal trajectory (straight movement) began increasing before the moment of target detection. It increased earlier and overall was larger for targets in unusual locations, indicating a competition between responses early on. Furthermore, detection time increased x-deviation before the moment of target detection and through most of the mouse trajectory, and the effect was greater for targets in unusual location.
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