Perceived slant: a dissociation between perception and action

Perceived slant is grossly overestimated, such that 5 degrees hills look to be about 20 degrees. However, overestimation is found only in visual and verbal measures of apparent slant; action measures are accurate. This dissociation is consistent with several lines of research that suggest that there exist two perceptual processes, one for visually guided actions and another for explicit awareness. However, studies in other contexts have shown that analogous effects can be the result of differences in the task demands associated with the responses themselves as opposed to the processes underlying the responses. Two experiments are reported in which these alternatives were tested. Our results are consistent with the hypothesis that two perceptual processes underlie the dissociation between explicit awareness and visuomotor assessments of perceived slant.