Sarah H. Creem

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.

Two memories for geographical slant: separation and interdependence of action and awareness

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.

Seeing mountains in mole hills: geographical-slant perception

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.

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.

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.

Face-based luminance matching for perceptual colormap generation

Most systems used for creating and displaying colormap-based visualizations are not photometrically calibrated. That is, the relationship between RGB input levels and perceived luminance is usually not known, due to variations in the monitor, hardware configuration, and the viewing environment. However, the luminance component of perceptually based colormaps should be controlled, due to the central role that luminance plays in our visual processing. We address this problem with a simple and effective method for performing luminance matching on an uncalibrated monitor. The method is akin to the minimally distinct border technique (a previous method of luminance matching used for measuring luminous efficiency), but our method relies on the brains highly developed ability to distinguish human faces. We present a user study showing that our method produces equivalent results to the minimally distinct border technique, but with significantly improved precision. We demonstrate how results from our luminance matching method can be directly applied to create new univariate colormaps.

Spatial updating after imagined self and object movement: translation is similar to rotation

References Updating the positions of objects in space is easier after imagined viewer rotation compared to object rotation (Wraga, Creem, & Proffitt, 2000). The advantage remains even when the required self-rotation is physically impossible to perform (Creem, Wraga, & Proffitt, 2001). This ease of imagined self-rotation contrasts with the findings of research that has compared imagined and real rotation and translation. These studies suggest that updating is difficult after imagined self-rotation compared to imagined selftranslation (Presson & Montello, 1994; Rieser, 1989). The present studies examined whether the advantage for imagined selfversus object-rotation seen in previous studies was primarily a result of the rotational component, or whether this difference would be apparent in translation tasks as well. The studies compared imagined viewer and array translations in the sagittal and frontal planes. The results indicated a consistent advantage for imagined selftranslation versus array-translation.

Motor representations involved in perceiving tools and graspable non-tools: an fMRI study

•fMRI Acquisition »1.5 T Siemens Vision scanner »Gradient-echo EPI sequence »26 contiguous axial slices 4 mm thick with in-plane resolution of 2.6 x 2.6 mm »Whole brain acquisition »Maximum of 128 acquisitions •Activation Localization »Pearson’s correlation with Bonferroni correction (AFNI) »Registered to anatomical MRI and spatially normalized to Talairach atlas (AFNI) »ANOVA to compare Tools and Non-Tools •Task »Covertly name objects »Look at blurred images •Paradigm »Alternated epochs of Tools, Non-tools (NT) and Blurred Images (Control) »8 Pictures presented in each epoch (400 ms) followed by crosshair (1600 ms) Discussion Do we perceive objects relative to their potential for actions? A number of recent studies have found that observation and naming of common tools activates premotor areas in the absence of any motoric task (Chao & Martin, 2000; Grafton et al., 1997; Martin et al., 1996). Activity in this area has not been found in similar tasks involving other types of objects. A question exists as to whether premotor activity is associated with a tool’s semantic properties relating to action, or whether this activity is associated with automatic motor representations elicited by any objects that afford actions.