Maryjane Wraga

Imagining rotation by endogenous versus exogenous forces: distinct neural mechanisms.

Previous neuroimaging studies of mental image transformations have sometimes implicated motor processes and sometimes not. In this study, prior to neuroimaging the subjects either viewed an electric motor rotating an angular object, or they rotated the object manually. Following this, they performed the identical mental rotation task in which they compared members of pairs of such figures, but were asked to imagine the figures rotating as they had just seen the model rotate. When results from the two rotation conditions were directly compared, motor cortex (including area M1) was found to be activated only when subjects imagined the rotations as a consequence of manual activity. Thus, there are at least two, qualitatively distinct, ways to imagine objects rotating in images, and these different strategies can be adopted voluntarily.

Updating displays after imagined object and viewer rotations.

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.

Implicit transfer of motor strategies in mental rotation

Recent research indicates that motor areas are activated in some types of mental rotation. Many of these studies have required participants to perform egocentric transformations of body parts or whole bodies; however, motor activation also has been found with nonbody objects when participants explicitly relate the objects to their hands. The current study used positron emission tomography (PET) to examine whether such egocentric motor strategies can be transferred implicitly from one type of mental rotation to another. Two groups of participants were tested. In the Hand-Object group, participants performed imaginal rotations of pictures of hands; following this, they then made similar judgments of pictures of Shepard-Metzler objects. The Object-Object group performed the rotation task for two sets of Shepard-Metzler objects only. When the second condition in each group (which always required rotating Shepard-Metzler objects) was compared, motor areas (Area 6 and M1) were found to be activated only in the Hand-Object group. These findings suggest that motor strategies can be covertly transferred to imaginal transformations of nonbody objects.

Imagined rotations of self versus objects : An fMRI study

This study used functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying two types of spatial transformations: imagined object rotations and imagined rotations of the self about an object. Participants viewed depictions of single three-dimensional Shepard--Metzler objects situated within a sphere. A T-shaped prompt appeared outside of the sphere at different locations across trials. In the object rotation task, participants imagined rotating the object so that one of its ends was aligned with the prompt. They then judged whether a textured portion of the object would be visible in its new orientation. In the self rotation task, they imagined rotating themselves to the location of the T-prompt, and then judged whether a textured portion of the object would be visible from the new viewpoint. Activation in both tasks was compared to respective control conditions in which identical judgments were made without rotation. A direct comparison of self and object rotation tasks revealed activation spreading from left premotor to left primary motor (M1) cortex (areas 6/4) for imagined object rotations, but not imagined self rotations. In contrast, the self rotation task activated left supplementary motor area (SMA; area 6). In both transformations, activation also occurred in other regions. These findings provide evidence for multiple spatial-transformation mechanisms within the human cognitive system.

Spatial updating of virtual displays

In four experiments, we examined observers’ ability to locate objects in virtual displays while rotating to new perspectives. In Experiment 1, participants updated the locations of previously seen landmarks in a display while rotating themselves to new views (viewer task) or while rotating the display itself (display task). Updating was faster and more accurate in the viewer task than in the display task. In Experiment 2, we compared updating performance during active and passive self-rotation. Participants rotated themselves in a swivel chair (active task) or were rotated in the chair by the experimenter (passive task). A minimal advantage was found for the active task. In the final experiments, we tested similar manipulations with an asymmetrical display. In Experiment 3, updating during the viewer task was again superior to updating during the display task. In Experiment 4, we found no difference in updating between active and passive self-movement. These results are discussed in terms of differences in sources of extraretinal information available in each movement condition.

An fMRI study of imagined self-rotation

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.

Perception-Action Dissociations of a Walkable Müller-Lyer Configuration

These studies examined the role of spatial encoding in inducing perception-action dissociations in visual illusions. Participants were shown a large-scale Müller-Lyer configuration with hoops as its tails. In Experiment 1, participants either made verbal estimates of the extent of the Müller-Lyer shaft (verbal task) or walked the extent without vision, in an offset path (blind-walking task). For both tasks, participants stood a small distance away from the configuration, to elicit object-relative encoding of the shaft with respect to its hoops. A similar illusion bias was found in the verbal and motoric tasks. In Experiment 2, participants stood at one endpoint of the shaft in order to elicit egocentric encoding of extent. Verbal judgments continued to exhibit the illusion bias, whereas blind-walking judgments did not. These findings underscore the importance of egocentric encoding in motor tasks for producing perception-action dissociations.

Stereotype susceptibility narrows the gender gap in imagined self-rotation performance

Three studies examined the impact of stereotype messages on men’s and women’s performance of a mental rotation task involving imagined self-rotations. Experiment 1 established baseline differences between men and women; women made 12% more errors than did men. Experiment 2 found that exposure to a positive stereotype message enhanced women’s performance in comparison with that of another group of women who received neutral information. In Experiment 3, men who were exposed to the same stereotype message emphasizing a female advantage made more errors than did male controls, and the magnitude of error was similar to that for women from Experiment 1. The results suggest that the gender gap in mental rotation performance is partially caused by experiential factors, particularly those induced by sociocultural stereotypes.

Thinking outside the body: an advantage for spatial updating during imagined versus physical self-rotation.

Three studies examined effects of different response measures on spatial updating during self-rotation. In Experiment 1, participants located objects in an array with a pointer after physical self-rotation, imagined self-rotation, and a rotation condition in which they ignored superfluous sensorimotor signals. In line with previous research, updating performance was found to be superior in the physical self-rotation condition compared with the other 2. In Experiment 2, participants performed in identical rotation movement conditions but located objects by verbal labeling rather than pointing. Within the verbal modality, an advantage for updating during imagined self-rotation was found. In Experiment 3, participants performed physical and imagined self-rotations only and used a pointing response offset from their physical reference frames. Performance was again superior during imagined self-rotations. The results suggest that it is not language processing per se that improves updating performance but rather a general reduction of the conflict between physical and projected egocentric reference frames.

Imagining physically impossible self-rotations: geometry is more important than gravity

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 self-rotation advantage. Experiments 1-3 preserved a real or imagined orthogonal relationship between the viewer and the array, requiring a rotation in the observers transverse plane. Despite imagined self-rotations that defied gravity, a viewer advantage remained. Without this orthogonal relationship (Experiment 4), the viewer advantage was lost. We suggest that efficient transformation of the egocentric reference frame relies on the representation of body-environment relations that allow rotation around the observers principal axis. This efficiency persists across different and conflicting physical and imagined postures.