Category effects on the processing of plane-rotated objects

We examined the effects of plane rotations on the identification of exempla rs 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 degrees, 60 degrees, 120 degrees, a nd 180 degrees of clockwise rotation). The response time was found to depen d on stimulus category. In particular, whereas rotation effects were shown for animals, no effect at all was found for vegetables and only partial eff ects were found for inanimate objects. The unclear pattern found for inanim ate objects was further examined in experiment 3 where the orientation effe cts on the identification of two subsets of the inanimate category were stu died. The hypothesis of view-observation frequency was confirmed. In experi ment 4, line drawings of objects at different orientations were presented i n physically degraded versions. The minimum amount of visual information ne cessary to identify rotated stimuli was found to vary as a function of stim ulus category as well. Results are discussed, combining current research on both viewpoint-dependence/independence and neural systems involved in cate gory processing.