PubMed · 7464950
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M A Georgeson, M G Harris. 1981-02-26. Size constancy does not fail below half a degree.. https://doi.org/10.1038/289826a0
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A one-sided (monopole) version of the Müller-Lyer was used to assess the effect of response mode on the metric distortion associated with the illusion. Two different response modes were tested for comparability. The Operant Mode required the judgment of stimulus span to be indicated by marking a dot on the test page. The Comparison Mode required judgment of equality of two adjoining prepositioned spans. The perceptual effects with the comparison procedure are known to consist of underestimation of spans which are bounded by concave fin-sets and over-estimation of spans which are bounded by convex fin-sets. The question is whether the motor demands of the operant task produce an additional source of metric bias. Analysis indicate a very high correlation of judgments for the two modes of testing. Also, data with either mode of responding closely fit a linear model of the effect, and the model provides comparable index values for the concave and convex versions. These results should mitigate concern about potential motor bias from the operant method and encourage its use as a more efficient procedure for assessing metric distortion.
Stewart et al (1993, Perception 22 1227-1224) attempted to demonstrate that the ratio of angular speed to angular acceleration, [symbol see text]/[symbol see text], of the approaching object is preferred as the source of time-to-collision information to the ratio of visual angle to angular speed, [symbol see text]/[symbol see text]. It is demonstrated that this is not justified.
This study investigated the effects of figure context on the apparent length of a line. In Exp. 1, ten participants were asked to adjust the length of a comparison line to match a standard line enclosed within a rectangle. The participants consistently overestimated the length of the standard line, demonstrating the stretching effect of figure context on the apparent length of a line. In Exp. 2 (12 participants), the size of the context figure was varied and it had no significant influence on the magnitude of the context effect. In Exp. 3 (nine participants), the context effect was shown not only for squares and rectangles but also for other shapes of figures such as circles and 5-pointed stars. We discuss the possible mechanism of the figure-context effect within Gregory's (1970, 1978) misapplied constancy theory of visual illusions.