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Participants imagined rotating either themselves or an array of objects that surrounded them. Their task was to report on the egocentric position of an item in the array following the imagined rotation. The dependent measures were response latency and number of errors committed. Past research has shown that self-rotation is easier than array rotation. However, we found that imagined egocentric rotations were as difficult to imagine as rotations of the environment when people performed imagined rotations in the midsagittal or coronal plane. The advantages of imagined self-rotations are specific to mental rotations performed in the transverse plane.

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.

In six experiments we demonstrate that the vertical–horizontal illusion that is evoked when viewing photographs and line drawings is relatively small, whereas the magnitude of this illusion when large objects are viewed is at least twice as great. Furthermore, we show that the illusion is due more to vertical overestimation than horizontal underestimation. The lack of a difference in vertical overestimation between pictures and line drawings suggests that vertical overestimation in pictures depends solely on the perceived physical size of the projection on the picture surface, rather than on what is apparent about an object's represented size. The vertical–horizontal illusion is influenced by perceived physical size. It is greater when viewing large objects than small pictures of these same objects, even when visual angles are equated.

We present an experiment on cooperative bimanual action. Right-handed subjects manipulated a pair of physical objects, a tool and a target object, so that the tool would touch a target on the object @g. 1). For this task, there is a marked specialization of the hands. Performance is best when the left hand orients the target object and the right hand manipulates the tool, but is significantly reduced when these roles are reversed. This suggests that the right hand operates relative to the frame-of-reference of the left hand. Furthermore, when physical constraints guide the tool placement, this fundamentally changes the type of motor control required. The task is tremendously simplified for both hands, and reversing roles of the hands is no longer an important factor. Thus, specialization of the roles of the hands is significant only for skilled manipulation.

We investigate the synergy of the two hands for virtual object manipulation. We report results from an experiment which suggest that the two hands together provide sufficient perceptual cues to form a frame of reference which is independent of visual feedback. The same is not true for one hand moving in empty space. Our interpretation is that users may not have to constantly maintain visual attention when both hands can be involved in a manipulation. Our results suggest that using two hands can provide more than just a time savings over one-handed manipulation. Two hands together provide the user with information which one hand alone cannot. Our results also suggest that using two hands can potentially impact performance at the cognitive level by changing how users think about a task. Since the user can potentially integrate subtasks controlled by each hand without an explicit cost to switch between subtasks, this encourages exploration of the task solution space. Finally, to illustrate why one might expect this to be true, we present a task analysis which helps to reason about the differences between one and two-handed interfaces.

We report results from a formal user study of interactive 3D rotation using the mouse-driven Virtual Sphere and Arcball techniques, as well as multidimensional input techniques based on magnetic orientation sensors. MultidimensionaI input is often assumed to allow users to work quickly, but at the cost of precision, due to the instability of the hand moving in the open air. We show that, at least for the orientation matching task used in this experiment, users can take advantage of the integrated degrees of freedom provided by multidimensional input without necessarily sacrificing precision: using multidimensional input, users completed the experimental task up to 36% faster without any statistically detectable loss of accuracy. We also report detailed observations of common usability problems when first encountering the techniques. Our observations suggest some design issues for 3D input devices. For example, the physical form-factors of the 3D input device significantly influenced user acceptance of otherwise identical input sensors. The device should afford some tactile cues, so the user can feel its orientation without looking at it. In the absence of such cues, some test users were unsure of how to use the device.

Virtual Reality (VR) has generated much excitement but little formal proof that it is useful. Because VR interfaces are difficult and expensive to build, the computer graphics community needs to be able to predict which applications will benefit from VR. In this paper, we show that users with a VR interface complete a search task faster than users with a stationary monitor and a hand-based input device. We placed users in the center of the virtual room shown in Figure 1 and told them to look for camouflaged targets. VR users did not do significantly better than desktop users. However, when asked to search the room and conclude if a target existed, VR users were substantially better at determining when they had searched the entire room. Desktop users took 41% more time, re-examining areas they had already searched. We also found a positive transfer of training from VR to stationary displays and a negative transfer of training from stationary displays to VR.

Publisher Summary An event is an occurrence entailing change over time. Visually perceivable events involve moving objects, observers, or both. Because events encompass just about everything that occurs in our everyday lives, one might reasonably wonder how event perception came to be a distinct topic within the field of visual space perception. Historically, the distinction arose between those perceptions that could be based on static optical information and those that could not. The chapter discusses the perceptions of space from primary and secondary depth cues that are typically taken to be distinct topics. Moreover, the perceptions of depth obtained from observing object rotations and motion parallax have received so much individual attention that they are distinct topics in their own right. Events are omnipresent in the phenomenology of everyday experience. Indeed, awareness seems to be composed entirely of events. Even when one observes a completely stationary surrounding, he or she arrived on the scene by locomotion and observe it with moving eyes, heads, and bodies. Most natural environments possess some moving objects, with animate creatures being of special interest.

Head-mounted displays, as popularized by virtual reality systems, offer the opportunity to immerse a user in a synthetically generated environment. While there is much anecdotal evidence that this is a qualitative jump in the user interface, there is little quantitative data to establish that emersion improves task performance. The authors present the results of a user study: users performing a generic search task decrease task performance time by roughly half (42% reduction) when they change from a stationary display to a head-mounted display with identical properties (resolution, field-of-view, etc.). A second result is that users who practice with the head-mounted display reduce task completion time by 23% in later trials with the stationary display, suggesting a transfer effect. >

Perception is a biological phenomenon and, as such, it is hierarchically organized and controlled. Research on biological systems requires a consideration of three levels of analysis: (1) the focal level of interest, (2) its initiating conditions, and (3) its boundary conditions. The information that flows into a focal level defines its initiating conditions. Light, for example, is an initiating condition for a photoreceptor. The response of a focal level to its initiating conditions can be discovered by studying the short-run behavior of the system in controlled contexts. In everyday contexts, the information flowing into a focal level is also constrained, prior to its reception, by boundary conditions imposed by the internal and external environment in which the focal level exists. The ways of life, experience, and current purposes of an organism place restrictions on how the available information will be sampled. Such boundary conditions are historically determined and can only be understood by examining the long-run behavior of the system in naturally occurring contexts.

This study examined the effect of physical display size on spatial knowledge of a virtual environment (VE). Previous research by Tan (2004) found that performance for a path integration task in a VE was superior on a large display compared to a small one, even with visual angle held constant. This may be because large displays evoke a more egocentric frame of reference than small displays. To test whether the advantages of large displays extended to a navigation transfer task, the present studies examined the effect of display size on transferring knowledge about the spatial layout of a desktop VE to virtual reality (VR). Participants used a joystick to control their movement through a virtual city environment, finding and learning the locations of five targets separated by buildings. After 20 minutes of learning, participants’ spatial knowledge was tested in a fully immersive environment by using virtual reality. Participants stood at each target location and pointed to each of the other, unseen targets. In the first study participants learned the VE on either an 18” LCD display or a 112” projected display. Visual angle was not equated. In the second study participants learned the VE on either a 25” or 72” projected display and visual angle was held constant. In both studies we found the average angular pointing error was significantly lower on the large display. Our results suggest that the advantage of a large desktop display for a virtual environment transfers to VR and is not dependent on visual angle. Bigger is Better: Large Visual Displays Improve Spatial Knowledge of a Virtual Environment

Recent developments in microelectronics have encouraged the use of 3D data bases to create compelling volumetric renderings of graphical objects. However, even with the computational capabilities of current-generation graphical systems, real-time displays of such objects are difficult, particularly when dynamic spatial transformations are involved. In this paper we discuss a type of visual stimulus (the stereokinetic effect display) that is computationally far less complex than a true three-dimensional transformation but yields an equally compelling depth impression, often perceptually in discriminable from the true spatial transformation. Several possible applications for this technique are discussed (e.g., animating contour maps and air traffic control displays so as to evoke accurate depth percepts).

In five experiments, assessments were made of people's understandings about the dynamics of wheels. It was found that undergraduates make highly erroneous dynamical judgments about the motions of this commonplace event, both in explicit problem-solving contexts and when viewing ongoing events. These problems were also presented to bicycle racers and high-school physics teachers; both groups were found to exhibit misunderstandings similar to those of naive undergraduates. Findings were related to our account of dynamical event complexity. The essence of this account is that people encounter difficulties when evaluating the dynamics of any mechanical system that has more than one dynamically relevant object parameter. A rotating wheel is multidimensional in this respect: in addition to the motion of its center of mass, its mass distribution is also of dynamical relevance. People do not spontaneously form the essential multidimensional quantities required to adequately evaluate wheel dynamics.

•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.

We studied the role of the horizon line as a source of information about the relative size of objects at a distance. Relative-size judgements (2AFC) were collected for two objects at 30.5 m and 23.8 m away from the observer to assess how performance depends on the relationship between the size of the objects and the eye level of the observer. In three experiments in an indoor hallway and in one experiment outdoors, accuracy was higher for objects in the neighbourhood of eye level. We consider these results in the light of two hypotheses: one which proposes that observers localise the horizon as a reference for judging relative size, ie on the basis of the horizon ratio, and another which proposes that observers perceive the general neighbourhood of the horizon and then employ a height-in-visual-field heuristic. The finding that relative-size judgements are best around the horizon implies the use of information independent of distance perception in perceiving size.

Two experiments assessed infant sensitivity to figural coherence in point-light displays moving as if attached to the major joints of a walking person. Experiment 1 tested whether 3- and 5-month-old infants could discriminate between upright and inverted versions of the walker in both moving and static displays. Using an infant-control habituation paradigm, it was found that both ages discriminated the moving but not the static displays. Experiment 2 was designed to clarify whether or not structural invariants were extracted from these displays. The results revealed that (1) moving point-light displays with equivalent motions but different topographic relations were discriminated while (2) static versions were not, and (3) arrays that varied in the amount of motion present in different portions of the display were also not discriminated. These results are interpreted as indicating that young infants are sensitive to figural coherence in displays of biomechanical motion.