Influence of Prior Visual Information on Exploratory Movement Direction in Texture Perception.

When humans explore objects haptically, they seem to use prior as well as sensory information to adapt their exploratory behavior [1]. For texture discrimination, it was shown that participants adapted the direction of their exploratory movement to be orthogonal to the orientation of textures with a defined direction [2]. That is, they adapted the exploratory direction based on the sensory information gathered over the course of an exploration, and this behavior improved their perceptual precision. In the present study we examined if prior visual information that indicates a texture orientation produces a similar adjustment of exploratory movement direction. We expected an increase of orthogonal initial exploration movements with higher qualities of prior information. In each trial, participants explored two grating textures with equal amplitude, only differing in their spatial period. They had to report the stimulus with the higher spatial frequency. Grating stimuli were given in six different orientations relative to the observer. Prior visual information on grating orientation was given in five different qualities: 50% (excellent information), 35%, 25%, 15% and 0% (no information). We analyzed movement directions of the first, middle and last strokes over the textures of each trial. The results show an increase in the amount of initial orthogonal strokes and a decrease in variability of movement directions with higher qualities of prior visual information.