VIEWPOINT-DEPENDENT MECHANISMS IN VISUAL OBJECT RECOGNITION - REPLY TO TARR AND BULTHOFF (1995)

I. Biederman and P. C. Gerhardstein (1993) demonstrated that a represe ntation specifying a distinctive arrangement of viewpoint-invariant pa rts (a geon structural description, [GSD]) dramatically reduced the co sts of rotation in depth. M. J. Tarr and H. H. Bulthoff (1995) attempt to make a case for viewpoint-dependent mechanisms, such as mental rot ation. heir suggestion that GSDs enjoy no special status in reducing t he effects of depth rotation is contradicted by a wealth of direct exp erimental evidence as well as an inadvertent experiment that found no evidence for the spontaneous employment of mental rotation. Their comp laint against geon theory's account of entry-level classification rest s on a mistaken and unwarranted attribution that geon theory assumes a one-to-one correspondence between GSDs and entry-level names. GSDs pr ovide a representation that distinguishes most entry- and subordinate- level classes and explains why complex objects are described as an arr angement of viewpoint-invariant parts.