Janice E. Murray

The proposal that identification of inverted objects is accomplished by either a relatively slow rotation in the picture plane or a faster rotation in the depth plane about the horizontal axis was tested. In Experiment 1, subjects decided whether objects at 0° or 180° corresponded to previously learned normal views of the upright objects, or were mirror images. Instructions to mentally flip an inverted object in the depth plane to the upright produced faster decision times than did instructions to mentally spin the object in the picture plane. In Experiment 2, the effects of orientation were compared across an object-naming task and a normal-mirror task for six orientations from 0° to 300°. In the normal-mirror task, objects at 180° were cued for rotation in the picture plane or in the depth plane in equal numbers. The naming function for one group of subjects did not differ from the normalmirror function where inverted objects had been mentally rotated to the upright. For both functions, response time (RT) increased linearly from 0° to 180° and the slopes did not differ. The naming function for a second group of subjects did not differ from the normal-mirror function where inverted objects had been mentally flipped to the upright. For both functions, RT increased linearly at a similar rate from 0° to 120°, but decreased from 120° to 180°. The results are discussed in terms of theories of orientation-specific identification.

Previous work has found that repeated exposure to ignored rotated objects is insufficient to allow the formation of orientation-invariant representations (Murray, 1995b). In this study, the negative priming paradigm was used to examine whether the identity of ignored rotated objects was encoded. Subjects were briefly presented with a prime followed by a probe display. One of the two overlapping drawings of objects in each display was selected for further processing, and the other was ignored. In one condition, the ignored objects were upright; in another, they were rotated 240°; and in a final condition, subjects repeatedly named the 240° objects prior to experiencing them as ignored objects in the priming task. Naming latency for the attended probe was slower when it was semantically related to the ignored prime in all conditions. The results suggest that unattended rotated objects are processed to a level of representation that is at least categorical.

The present experiment examined whether subjects can form and store imagined objects in various orientations. Subjects in a training phase named line drawings of natural objects shown at six orientations, named objects shown upright, or imagined upright objects at six orientations. Time to imagine an upright object at another orientation increased the farther the designated orientation was from the upright, with faster image formation times at 180° than at 120°. Similar systematic patterns of effects of orientation on identification time were found for rotated objects. During the test phase, all subjects named the previously experienced objects as well as new objects, at six orientations. The orientation effect for old objects seen previously in a variety of orientations was much reduced relative to the orientation effect for new objects. In contrast, substantial effects of orientation on naming time were observed for old objects for subjects who had previously seen the objects upright only or upright but imagined at different orientations. The results suggest that the attenuation of initially large effects of orientation with practice cannot be due to imagining and forming representations of objects at a number of orientations.