A parallel between visual and haptic perception of size at a distance

In the haptic perception of the size of frontoparallel intervals achieved by probing between two objects with a handheld stick, perceived size decreases with distance, with the rate of decrease greater for greater sizes. Analysis and experimentation have shown that these perceptual results are predicted by a quantity that is invariant over probing and specific to the physical conditions defined by the spatial layout and the probe. In this article, we conjecture that an analogous quantity may be involved in the visual perception of size at a distance. Preliminary to the pursuit of this analogous quantity is the demonstration that visual perception reveals the same dependencies on size and distance as extended haptic perception. In Experiment 1, the haptic and visual perceptions of frontoparallel intervals were compared under similar conditions, and in Experiment 2, the range of such intervals to be perceived visually was extended. The standard results for extended haptic perception were replicated and the same pattern was found in both experiments for visual perception. Discussion focused on the various interpretations of ''visual space,'' methodological issues in experiments on size perception, and the possibility of a similar basis to size perception haptically and visually.