Category effects on the processing of plane-rotated objects.

We examined the effects of plane rotations on the identification of exemplars of three semantic categories. In the first two experiments line drawings belonging to three categories (animals, inanimate objects, and vegetables) were presented at four orientations (0 degree, 60 degrees, 120 degrees, and 180 degrees of clockwise rotation). The response time was found to depend on stimulus category. In particular, whereas rotation effects were shown for animals, no effect at all was found for vegetables and only partial effects were found for inanimate objects. The unclear pattern found for inanimate objects was further examined in experiment 3 where the orientation effects on the identification of two subsets of the inanimate category were studied. The hypothesis of view-observation frequency was confirmed. In experiment 4, line drawings of objects at different orientations were presented in physically degraded versions. The minimum amount of visual information necessary to identify rotated stimuli was found to vary as a function of stimulus category as well. Results are discussed, combining current research on both viewpoint-dependence/independence and neural systems involved in category processing.