Viewpoint-Dependent Mechanisms in Visual Object Recognition: Reply to Tarr and Biilthoff (1995)

I. Biederman and P. C. Gerhardstein (1993) demonstrated that a representation specifying a distinctive arrangement of viewpoint-invariant parts (a geon structural description, [GSD]) dramatically reduced the costs of rotation in depth. M. J. Tarr and H. H. Bulthoff (1995) attempt to make a case for viewpoint-dependent mechanisms, such as mental rotation. Their suggestion that GSDs enjoy no special status in reducing the effects of depth rotation is contradicted by a wealth of direct experimental evidence as well as an inadvertent experiment that found no evidence for the spontaneous employment of mental rotation. Their complaint against geon theory's account of entry-level classification rests on a mistaken and unwarranted attribution that geon theory assumes a one-to-one correspondence between GSDs and entry-level names. GSDs provide a representation that distinguishes most entryand subordinate-level classes and explains why complex objects are described as an arrangement of viewpoint-invariant parts.