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Judging distance without a continuously textured ground surface
Abstract
According to Gibson's (1950) ground theory, continuous surfaces provide the basis for visual distance
perception. One implication of this theory is that distance perception will be impaired when a continuously
textured ground surface is not present. Accordingly, Sinai, Ooi, and He (Nature, 1998) found that judged
distance along a ground plane was reduced when the ground surface consisted of two different textures.
The purpose of the present study was to examine the types of texture discontinuities that affect exocentric
distance judgments along a ground surface. Observers viewed displays of a moving scene consisting of a
ground plane and three vertical poles. The plane was either continuously textured or was divided along the
depth dimension into two or three differently textured areas. Observers judged the distance between two
poles that were separated in depth by adjusting the separation of two poles that were separated horizontally.
In the first experiment, judged depth separation was reduced when the poles were located in regions of
different texture, replicating Sinai et al.'s result. In the second experiment, we found that judged depth
separation was reduced even with the poles in areas with the same texture, if a region with a different
texture was located between the poles being judged. In the third experiment, the same parallel line texture
was used in both regions, but the regions were offset horizontally, producing a discontinuity at the border.
We found that a discontinuity, without a change in texture, is sufficient to reduce the judged depth
separation. Overall, these results provide evidence that any discontinuity in the texture of the ground
surface, even if it does not involve a change in the type of texture, reduces judged distance along the
ground plane.
Supported by NIH Grant 1R01EY12437.
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