Time and intensity as determiners of perceived shape.

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Abstract
The function relating matched shape to exposure duration and to luminance was determined for human subjects by matching ellipses with an obliquely viewed disc. For near threshold stimulus conditions, the axis ratios of matched ellipses are in agreement with predictions made on the basis of geometrical optics. With increase in either duration or luminance, the matched axis ratios become larger exhibiting the tendency towards shape constancy. The functions increase rapidly at first, and then more slowly, before approaching a limiting value. The diminution of the tendency toward perceptual constancy resulting from reduction of luminance is attributed to the impairment of visual acuity and intensity discrimination for the "additional" stimuli in the visual field. Some of the variation due to reduction of exposure time can be attributed to the reciprocal relation between time and intensity (Bunsen-Roscoe law). However, there is an effect both above and below critical duration which represents the influence of exposure time as a determiner of perceived shape in addition to its role in the reciprocity relationship. Eye movement records, taken while the subjects were making shape judgments, confirm the finding that an exposure duration longer than the critical duration is required to produce the maximum tendency toward shape constancy.

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