Discrimination of planar surface slant from texture: human and ideal observers compared

In order to quantify the ability of the human visual system to use texture information to perceive planar surface orientation, I measured subjects' ability to discriminate planar surface slant (angle away from the fronto-parallel) for a variety of different types of textures and in a number of different viewing conditions. I measured the subjects' discrimination performance as a function of surface slant, field of view size and surface texture structure. I compared the subjects' performance with that of ideal observers derived for each of the available texture cues--texel position, scaling and foreshortening. The results can be summarized by four points: (i) subjects' discrimination performance improves dramatically with increasing surface slant, tracking the performance of the ideal observers; (ii) subjects can integrate texture information over a large range of visual angles; (iii) comparisons between human subjects and ideal observers show that the human observers rely to some degree on foreshortening information; and (iv) similar comparisons show that in using foreshortening information, subjects rely to some extent on a prior assumption of isotropy.