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要旨

Previous studies have shown that visual perception of geographical slant is greatly overestimated (Proffitt et al., 1995). These studies positioned the observer's viewpoint near to the hill. Phenomenal experience often results in more distant hills looking “even steeper” than nearer slopes. This is consistent with a computational analysis which predicts that visual information for a slope is reduced with viewing distance. We conducted a study to systematically examine this phenomenon by varying observers' viewing distance from real hills and assessing perceptual and action-based measures of geographical slant. Participants viewed grassy hills from the base of the hill or from 70 meters away. They gave three estimates of the slant of the hill: a verbal judgment in degrees, a visual matching judgment, and a haptic adjustment of a tilting board with their unseen hand. The results indicated an increase in verbal, visual, and haptic judgments for the far versus near distance. These findings differ from previous studies that have typically found accurate haptic responses despite manipulations that have led to increased overestimation in verbal and visual responses. In the present study, manipulating viewing distance from the hill influenced both the available information for slant and whether a hill may be directly acted upon. The consistent increase for the three estimations suggests that when a hill falls outside of one's “action space”, motoric and perceptual responses may be informed by the same perceptual representation. Additional manipulations of farther viewing distances and availability of visual cues are needed to more fully account for this phenomenon.