PubMed · 5482577
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H Taijfel. 1970. Experiments in intergroup discrimination.. https://pubmed.ncbi.nlm.nih.gov/5482577/
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Under normal viewing conditions we are little conscious of blur in moving objects, despite the persistence of vision. Moving objects look more blurred in brief than in long exposures, suggesting an active mechanism for suppressing motion blur. To see whether blur suppression would improve visual discrimination of objects, we measured blur discrimination thresholds for moving Gaussian-blurred edges and bars. The observer's task was to decide which of two moving stimuli, presented successively, was the more blurred. It is known that for stationary objects the just-noticeable difference in blur increases with baseline blur; therefore, if motion increases blur, it would be expected to increase the just-noticeable difference in blur. An active deblurring mechanism, on the other hand, would be expected to counteract the detrimental effects of motion blur on discrimination performance. We found, however, that motion increased thresholds for blur discrimination, both for brief (40 ms) and for longer (150 ms) exposures. We conclude that motion deblurring is a subjective effect, which does not enhance visual discrimination performance. Moving objects appear sharp, not because of some special mechanism that removes blur, but because the visual system is unable to perform the discrimination necessary to decide whether the moving object is really sharp or not.
A major determinant of human texture segregation and discrimination is the orientational content of the stimuli used. We have investigated the ability of observers to resolve features defined in the orientation domain in a variety of textures. It was found that features had to be separated by at least 13 deg for subjects to discriminate orientationally bimodal textures from same-variance unimodal textures. For larger separations, the determinant of performance was the magnitude of the central "dip" in the probability density functions determining the bimodal textures. Resolution performance can be modelled by assuming that a filtering process over orientation demodulates the central dip in the bimodal texture and that discrimination depends on criterion depth in the resulting function. Such modelling produces relatively broad estimates of the bandwidth ranging from about 10-20 deg. Performance was similar for both line and Gabor micropattern stimuli.
Direction discrimination (upward/downward or left/right) for a Gabor patch in a two-frame motion display was measured as a function of the inter-frame displacement size of the component grating with the stimulus position (center, left, right, upper and lower visual fields) as a parameter. The results showed that, for vertical motion in the center, left, right and lower visual fields, the observers saw downward motion more frequently than upward motion, whereas for vertical motion in the upper field and for horizontal motion, no preference for one of the two opposite directions was obtained. Human motion vision is anisotropic in the lower half of the visual field.