Abstract
The human visual system is anisotropic not only for stimulus detection and discrimination but also for stimulus appearance. The apparent length of a stationary stimulus and the apparent velocity of a moving stimulus vary with orientation. These variations are predictable from a model assuming a compression of the horizontal spatial meridian relative to the vertical meridian. In this paper, the apparent spatial frequency of a suprathreshold grating is shown to depend on the grating orientation. Specifically, horizontal gratings appear coarser than vertical gratings of equivalent spatial frequency. Additional data collected from the same group of observers show that horizontal lines appear shorter than vertical lines of the same extent. The presence of the spatial frequency and length illusions, although both predictable from the compression model, were not found to be correlated within observers. Implications of these results for other data in the literature are discussed.
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This research was funded in part by National Eye Institute Grant EY-01319 awarded to the Center for Visual Science.
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Bowker, D.O. Variations in apparent spatial frequency with stimulus orientation: L Incidence of the effect in the general population. Perception & Psychophysics 29, 563–567 (1981). https://doi.org/10.3758/BF03207372
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DOI: https://doi.org/10.3758/BF03207372