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Lynn Olzak, Patrick Hibbeler, Thomas Wickens; Do illusory contours prevent spatial interactions?. Journal of Vision 2010;10(7):1369. doi: 10.1167/10.7.1369.
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In the third of a series of concurrent-response experiments examining decision processes in fine spatial discriminations, we have investigated the effect of creating an illusory contour between a center grating patch and a surrounding grating annulus by shifting the relative phase of the two by 180 deg. In single-response paradigms, the phase shift appears to render the two stimulus parts independent (Saylor & Olzak, 2006). Four stimuli were intermingled into a single session of 160 trials. In different conditions of the experiment, observers either made hyperacuity-level orientation or spatial frequency judgments. Both the center and surround grating patches contained a cue to discrimination; for example, left-left, right-right, left-right and right-left. Observers made two consecutive judgments, one on the center and one on the surround (order was counterbalanced across observers), rating their confidence on a 6-point scale that either Pattern A ( e.g. left) or Pattern B (e.g. right) was presented in that part of the stimulus. Like previous results found with in-phase abutting stimuli and those separated by a tiny gap, independent processing was strongly rejected. Observers appeared once again to be using a complex decision strategy in which they first classified the stimulus as the “same” type (left-left or right-right) or of the “different” type (left-right or right-left), and then using the rating scale in a correlated or anti-correlated way for the two decisions. We discuss these findings in the context of General Recognition Theory (Ashby & Townsend, 1986). Saylor, S. A. and Olzak, L. A. (2006) Contextual effects on fine orientation discrimination tasks. Vision Research, 46 (18), 2988-2997. Ashby, F. G and Townsend J. T. (1986) Varieties of perceptual independence. Psychological Review, 93, 154-179.
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