Six experiments compared spatial updating of an array after imagined rotations of the array versus viewer. Participants responded faster and made fewer errors in viewer tasks than in array tasks while positioned outside (Experiment 1) or inside (Experiment 2) the array. An apparent array advantage for updating objects rather than locations was attributable to participants imagining translations of single objects rather than rotations of the array (Experiment 3). Superior viewer performance persisted when the array was reduced to 1 object (Experiment 4); however, an object with a familiar configuration improved object performance somewhat (Experiment 5). Object performance reached near-viewer levels when rotations included haptic information for the turning object. The researchers discuss these findings in terms of the relative differences in which the human cognitive system transforms the spatial reference frames corresponding to each imagined rotation.Suppose you are playing a board game with a group of friends, and you want to know what the board looks like from one of their perspectives, without moving to it. There are two obvious ways to proceed. You could imagine rotating the board until the side corresponding to the new perspective is coincident with your current viewpoint (object rotation). Alternatively, you could imagine moving yourself to the vantage point of the new perspective (viewer rotation). Both operations have been implicated in human beings 1 ability to update objects and scenes across views (e.g.,

Research has illustrated dissociations between "cognitive" and "action" systems, suggesting that different representations may underlie phenomenal experience and visuomotor behavior. However, these systems also interact. The present studies show a necessary interaction when semantic processing of an object is required for an appropriate action. Experiment 1 demonstrated that a semantic task interfered with grasping objects appropriately by their handles, but a visuospatial task did not. Experiment 2 assessed performance on a visuomotor task that had no semantic component and showed a reversal of the effects of the concurrent tasks. In Experiment 3, variations on concurrent word tasks suggested that retrieval of semantic information was necessary for appropriate grasping. In all, without semantic processing, the visuomotor system can direct the effective grasp of an object, but not in a manner that is appropriate for its use.

The present study extended previous findings of geographical slant perception, in which verbal judgments of the incline of hills were greatly overestimated but motoric (haptic) adjustments were much more accurate. In judging slant from memory following a brief or extended time delay, subjects' verbal judgments were greater than those given when viewing hills. Motoric estimates differed depending on the length of the delay and place of response. With a short delay, motoric adjustments made in the proximity of the hill did not differ from those evoked during perception. When given a longer delay or when taken away from the hill, subjects' motoric responses increased along with the increase in verbal reports. These results suggest two different memorial influences on action. With a short delay at the hill, memory for visual guidance is separate from the explicit memory informing the conscious response. With short or long delays away from the hill, short-term visual guidance memory no longer persists, and both motor and verbal responses are driven by an explicit representation. These results support recent research involving visual guidance from memory, where actions become influenced by conscious awareness, and provide evidence for communication between the "what" and "how" visual processing systems.Hills appear steeper than they actually are, an intriguing phenomenon recently described by Proffitt, Bhalla, Gossweiler, and Midgett (1995). For example, a 5°hill is consistently judged to be about 20°. Although people judge hills to be much steeper than they actually are, they can traverse them with no difficulty. Despite an exaggeration in conscious perceptual judgment, people do not manifest this overestimation in a visually guided action directed toward the hill. Proffitt et al. showed that a motoric (haptic) adjustment of slant did not reflect the overestimation seen in conscious reports ofthe hill inclination. They proposed that the perceived exaggeration of geographical slant preserves the relationship between distal inclination and people's behavioral potential. The steepness of a hill that one perceives gives the observer information about the effort required to traverse that hill. Furthermore, Proffitt et al. suggested that the differences between verbal and motoric estimates of hill slants illustrate the separation of the visual pathways that mediate conscious perception and visually guided action.We recently asked people to judge the slants of familiar hills from memory. We found that people remembered hills to be even steeper than they had perceived them to be. This research was supported by NIMH Grant MH52640 and NASA Grant NCC-2-925 to D. R. P. The authors wish to thank Mukul Bhalla for many discussions of ideas, Arthur Shulman for providing valuable comments on an earlier version of this paper, and Valerie Lewis and Gavin Sacks for their help in running the experiments. Correspondence should be addressed to S. H. Creem, Department of Psychology, 102 Gilmer Hall, University of Virginia, Charlottesville, ...

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When observers face directly toward the incline of a hill, their awareness of the slant of the hill is greatly overestimated, but motoric estimates are much more accurate. The present study examined whether similar results would be found when observers were allowed to view the side of a hill. Observers viewed the cross-sections of hills in real (Experiment 1) and virtual (Experiment 2) environments and estimated the inclines with verbal estimates, by adjusting the cross-section of a disk, and by adjusting a board with their unseen hand to match the inclines. We found that the results for cross-section viewing replicated those found when observers directly face the incline. Even though the angles of hills are directly evident when viewed from the side, slant perceptions are still grossly overestimated.

In the present study, functional magnetic resonance imaging was used to examine the neural mechanisms involved in the imagined spatial transformation of one's body. The task required subjects to update the position of one of four external objects from memory after they had performed an imagined self-rotation to a new position. Activation in the rotation condition was compared with that in a control condition in which subjects located the positions of objects without imagining a change in selfposition. The results indicated similar networks of activation to other egocentric transformation tasks involving decisions about body parts. The most significant area of activation was in the left posterior parietal cortex. Other regions of activation common among several of the subjects were secondary visual, premotor, and frontal lobe regions. These results are discussed relative to motor and visual imagery processes as well as to the distinctions between the present task and other imagined egocentric transformation tasks.

Previous studies found that it is easier for observers to spatially update displays during imagined self-rotation versus array rotation. The present study examined whether either the physics of gravity or the geometric relationship between the viewer and array guided this selfrotation advantage. Experiments 1±3 preserved a real or imagined orthogonal relationship between the viewer and the array, requiring a rotation in the observer's transverse plane. Despite imagined self-rotations that de®ed gravity, a viewer advantage remained. Without this orthogonal relationship (Experiment 4), the viewer advantage was lost. We suggest that ef®cient transformation of the egocentric reference frame relies on the representation of body±environment relations that allow rotation around the observer's principal axis. This ef®ciency persists across different and con¯icting physical and imagined postures. q

The human visual system can represent an object's spatial structure with respect to multiple frames of reference. It can also utilize multiple reference frames to mentally transform such representations. Recent studies have shown that performance on some mental transformations is not equivalent: Imagined object rotations tend to be more dicult than imagined viewer rotations. We reviewed several related research domains to understand this discrepancy in terms of the dierent reference frames associated with each imagined movement. An examination of the mental rotation literature revealed that observersÕ diculties in predicting an objectÕs rotational outcome may stem from a general de®cit with imagining the cohesive rotation of the objectÕs intrinsic frame. Such judgments are thus more reliant on supplementary information provided by other frames, such as the environmental frame. In contrast, as assessed in motor imagery and other studies, imagined rotations of the viewerÕs relative frame are performed cohesively and are thus mostly immune to eects of other frames. Ó 1999 Elsevier Science B.V. All rights reserved.