Apparent afterimage size, Emmert's law, and the role of oculomotor adjustments in object-centered perception

Lou, Liang (2006) Apparent afterimage size, Emmert's law, and the role of oculomotor adjustments in object-centered perception. In: 10th annual meeting of the Association for the Scientific Study of Consciousness, 23-26 June 2006, Oxford, UK.

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Abstract

To what extent does taking an analytical perceptual attitude lead to a viewer-centered rather than object-centered percept? In a series of experiments, the apparent size of an afterimage viewed from distances between 5cm to 580cm was matched to that of a size-adjustable stimulus at a fixed distance (20, 30, 90, and 200cm). The experiment was conducted in a room with normal illumination and with a procedure that facilitated ‘analytical attitude’----the mental set for perceiving the angular size of the object. The apparent size (in visual angle) was found to increase with the focusing distance within one meter and very little beyond one meter. Observations with an equivalent set of real stimuli with proportionally larger sizes at greater distances led to similar results. These results suggest that Emmert’s law fails as an accurate and useful description of the apparent afterimage size as a function of viewing distance. Following von Holst (1950), Leibowitz (1974) and Enright (1989), the results are interpreted as suggesting a distinct role of oculomotor adjustment for accommodation and convergence in size perception, in that it leads to visually apparent sizes that are more object-centered than viewer-centered, and more resistant to attitudinal influences than most optical cues.

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