Treading a Slippery Slope: Slant Perception In Near and Far Space


Hills are judged steeper with verbal measures than with motor measures. Previous studies of slope estimation have used relatively long distances. Since some neurons in premotor and parietal cortex respond only to objects within arm’s reach, this study was designed to compare verbal and motor estimates of slopes in near and far space. Verbal estimates greatly overestimated slopes (distance & surface experiment); the overestimates increased with distance from the participant by a log function (supplementary distance experiment). Participants continue to overestimate slopes after traversing hills to be estimated before judgment (contextual influence experiment), despite experiencing more accurate slope perception at near space; appearance trumps experience. The results can be interpreted as an implicit slope, previously measured only in darkness, modulated by depth cues available at near distances. We conclude that geometric layout of the world interacts with effort required for locomotion, but more strongly for verbal than for motor measures.

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