Orientation discrimination, tilt aftereffects, and the processing of luminance and illusory contours in human vision

Christopher J Bockisch, University of Pennsylvania

Abstract

A series of orientation judgment tasks sought evidence for separate processing mechanisms for luminance and the illusory contours perceived at collinear line-ends. The assumption was made that if a single mechanism supports the perception of both types of contours, then illusory and luminance contours that produce the same level of orientation discrimination will be equally effective adapting patterns in a tilt aftereffect experiment. A first experiment evaluated the possibility of matching orientation discrimination performance for illusory and luminance contours by comparing psychometric functions. The psycho-metric functions for illusory and luminance contours were very similar. Experiment II measured orientation discrimination for a range of line intensities for both contour types. Experiment III measured tilt aftereffects following adaptation to illusory and luminance contours that supported a similar range of orientation discrimination. The results reject the single mechanism model, as equal TAEs were not observed for illusory and luminance contours that supported a similar range of orientation discrimination performance. Experiments IV and V sought to validate the assumption that under a single mechanism model contours that support the same level of orientation discrimination should produce similar TAEs by using stimuli that seemed likely to be represented by the same visual mechanism. Luminance contours masked by randomly placed dots and unmasked luminance contours were used in the same orientation discrimination and tilt aftereffect procedures of experiments II and III. Equal TAEs were not observed for masked and unmasked contours matched on orientation discrimination, suggesting the original assumption was incorrect. Possible reasons for the failure are discussed.

Subject Area

Psychology|Experiments|Cognitive therapy

Recommended Citation

Bockisch, Christopher J, "Orientation discrimination, tilt aftereffects, and the processing of luminance and illusory contours in human vision" (1996). Dissertations available from ProQuest. AAI9627886.
https://repository.upenn.edu/dissertations/AAI9627886

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