Modal and amodal thin-fat Kanizsa shape discrimination with classification images in stereo R Liu1, Y Zhou1, Z Liu2 |
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1School of Life Sciences, University of Science and Technology of China, China |
| Purpose. We investigated thin-fat Kanizsa shape discrimination (Ringach and Shapley, 1996), using classification images (CIs) in stereo. We asked: (1) Are modal and amodal shape discriminations equally good? (2) To what extent does contour completion occur after binocular fusion? Method. The thin or fat Kanizsa shape was either in front of the inducers in depth (modal) or, when the left- and right-eye images were switched, behind four holes (amodal). Noise was added either to the inducer plane or, as control, to the Kanizsa shape plane. The luminance of the background and the contrast of the noise were fixed. The luminance of the inducers was adjusted so that thin-fat discrimination was 70.7% correct. For each condition 10,000 trials were run. Seven subjects participated. Results and conclusions. (1) The inducer contrast threshold was higher for amodal (0.31) than for modal (0.26) discrimination, p = 0.001, implying that their mechanisms were unlikely to be identical. (2) The CIs showed two vertical bands at the locations of the vertical contours of the Kanizsa shape, with an offset identical to the binocular disparity. This result suggests that contour completion took place before binocular fusion. The single bands in the control CIs further support this suggestion. |
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