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Motion fields differ in the degree to which they can serve as hierarchical frames of reference. To assess the strength of hierarchical motion organisation, we measured the ability of human observers to extract the motion of a target dot relative to a background of moving dots. The task was to discriminate circular from elliptical relative motions for the target dot (2AFC). Observers performed above chance for translational and divergence backgrounds, but were at chance level for rotational backgrounds. This finding, however, was based on random configurations of dots, where locations and trajectories were unrelated. When spatial constraints were introduced, observers used a different strategy and performed above chance also for rotational backgrounds. Both the effect of motion transformations and the effect of spatial information can be understood if we assume that the task is to find the most likely mechanical description of an object in a three-dimensional environment.

We argue that the experimental conditions in the Durgin et al. (2009) study were so different from those in Bhalla and Proffitt (1999) that the results of the former study cannot be generalized to the latter. The participants in the Durgin et al. study viewed a 2-m-long ramp; those in Bhalla and Proffitt viewed expansive hills. When drawing generalizations from one study to another, equating experimental conditions is always important; moreover, from an embodied perspective on perception, equating the opportunities for action also matters.

Previous studies have shown that conscious awareness of hill slant is overestimated, but visually guided actions directed at hills are relatively accurate. Also, steep hills are consciously estimated to be steeper from the top than the bottom, possibly because they are dangerous to descend. In the present study, participants stood at the top of a hill either on a skateboard or a wooden box of the same height. They gave three estimates of the slant: a verbal report, a visually matched estimate, and a visually guided action. Fear of descending the hill was also assessed. Those participants who were scared (by the skateboard) consciously judged the hill to be steeper than unafraid participants. However, the visually guided action measure was accurate across conditions. These results suggest that explicit awareness of slant is influenced by the fear associated with a potentially dangerous action that could be performed on the hill.

We discuss a two-handed user interface designed to support three-dimesional neurosurgical visualization. By itself, this system is a “point design,” an example of an advanced user interface technique. In this work, we argue that in order to understand why interaction techniques do or do not work, and to suggest possibilities for new techniques, it is important to move beyond point design and to introduce careful scientific measurement of human behavioral principles. In particular, we argue that the common-sense viewpoint that “two hands save time by working in parallel” may not always be an effective way to think about two-handed interface design because the hands do not necessarily work in parallel (there is a structure to two-handed manipulation) and because two hands do more than just save time over one hand (two hands provide the user with more information and can structure how the user thinks about a task). To support these claims, we present an interface design developed in collaboration with neurosurgeons which has undergone extensive informal usability testing, as well as a pair of formal experimental studies which investigate behavioral aspects of two-handed virtual object manipulation. Our hope is that this discussion will help others to apply the lessons in our neurosurgery application to future two-handed user interface designs.

Proffitt, Stefanucci, Banton, and Epstein (2003) reported a set of studies showing that the perceived distance to a target is influenced by the effort required to walk to its location. Hutchison and Loomis (H&L) reported an experiment that failed to find a significant influence of effort on indices of apparent distance. There were numerous important differences between the design and methods of H&L's study and those of Proffitt et al. Moreover, there are important theoretical reasons to believe that these differences were responsible for the different results. The theoretical motivation of H&L's studies was also brought into question.

While acknowledging that their design and methods were different from the original Proffitt, Stefanucci, Banton, and Epstein (2003) study, Hutchison and Loomis (H&L) continue to argue that their findings qualify our account of energetic influences on distance perception. This reply provides a brief and focused discussion of the methodological differences between their study and ours and why these differences were likely responsible for the different results. It is also argued that the measures employed by H&L are assessments of apparent location, not apparent distance.

The current study shows that people's ability to inhibit implicit associations that run counter to their explicit views varies in a circadian pattern. The presence of this rhythmic variation suggests the involvement of a biological process in regulating automatic associations--specifically, with the current data, associations that form undesirable social biases. In 1998, Greenwald, McGhee, and Schwartz introduced the Implicit Association Test as a means of measuring individual differences in implicit cognition. The IAT is a powerful tool that has become widely used. Perhaps most visibly, studies employing the IAT demonstrate that people generally hold implicit biases against social groups, which often conflict with their explicitly held views. The IAT engages inhibitory processes similar to those inherent in self-control tasks. Because the latter processes are known to be resource-limited, we considered whether IAT scores might likewise be resource dependent. Analyzing IAT performance from over a million participants across all times of day, we found a clear circadian pattern in scores. This finding suggests that the IAT measures not only the strength of implicit associations, but also the effect of variations in the physiological resources available to inhibit their undesirable influences on explicit behavior.

Survival for any organism, including people, is a matter of resource management. To ensure survival, people necessarily budget their resources. Spatial perceptions contribute to resource budgeting by scaling the environment to an individual’s available resources. Effective budgeting requires setting a balance of income and expenditures around some baseline value. For social resources, this baseline assumes that the individuals are embedded in their social network. A review of the literature supports the proposal that our visual perceptions vary based on the implicit budgeting of physical and social resources, where social resources, as they fluctuate relative to a baseline, can directly alter our visual perceptions.

The influence of color as a surface feature versus its influence as stored knowledge in object recognition was assessed. Participants decided whether a briefly presented and masked picture matched a test name. For pictures and words referring to similarly shaped objects, semantic color similarity (SCS) was present when picture and word shared the same prototypical color (e.g., purple apple followed by cherry). Perceptual color similarity (PCS) was present when the surface color of the picture matched the prototypical color of the named object (e.g., purple apple followed by blueberry). Response interference was primarily due to SCS, despite the fact that participants based similarity ratings on PCS. When uncolored objects were used, SCS interference still occurred, implying that the influence of SCS did not depend on the presence of surface color. The results indicate that, relative to surface color, stored color knowledge was more influential in object recognition.

Novel results elucidating the magnitude, binocularity and retinotopicity of aftereffects of visual texture density adaptation are reported as is a new contingent aftereffect of texture density which suggests that the perception of visual texture density is quite malleable. Texture aftereffects contingent upon orientation, color and temporal sequence are discussed. A fourth effect is demonstrated in which auditory contingencies are shown to produce a different kind of visual distortion. The merits and limitations of error-correction and classical conditioning theories of contingent adaptation are reviewed. It is argued that a third kind of theory which emphasizes coding efficiency and informational considerations merits close attention. It is proposed that malleability in the registration of texture information can be understood as part of the functional adaptability of perception.

People judged the inclination of hills viewed either out-of-doors or in a computer-simulated virtual environment. Angle judgments were obtained by having people (1) provide verbal estimates, (2) adjust a representation of the hill's cross-section, and (3) adjust a tilt board with their unseen hand. Geographical slant was greatly overestimated according to the first two measures, but not the third. Apparent slant judgments conformed to ratio scales, thereby enhancing sensitivity to the small inclines that must actually be traversed in everyday experience. It is proposed that the perceived exaggeration of geographical slant preserves the relationship between distal inclination and people's behavioral potential. Hills are harder to traverse as people become tired; hence, apparent slant increased with fatigue. Visually guided actions must be accommodated to the actual distal properties of the environment; consequently, the tilt board adjustments did not reflect apparent slant overestimations, nor were they influenced by fatigue. Consistent with the fact that steep hills are more difficult to descend than to ascend, these hills appeared steeper when viewed from the top.

The accuracy of depth judgments that are based on binocular disparity or structure from motion (motion parallax and object rotation) was studied in 3 experiments. In Experiment 1, depth judgments were recorded for computer simulations of cones specified by binocular disparity, motion parallax, or stereokinesis. In Experiment 2, judgments were recorded for real cones in a structured environment, with depth information from binocular disparity, motion parallax, or object rotation about the y-axis. In both of these experiments, judgments from binocular disparity information were quite accurate, but judgments on the basis of geometrically equivalent or more robust motion information reflected poor recovery of quantitative depth information. A 3rd experiment demonstrated stereoscopic depth constancy for distances of 1 to 3 m using real objects in a well-illuminated, structured viewing environment in which monocular depth cues (e.g., shading) were minimized.

Three fundamental questions are addressed: (1) What are the effective sources of optical information for perceiving spatial relationships and events? Complex natural environments provide a plethora of information potentially related to spatial layout. Psychophysical research investigates the efficacy and perceptual processing of these potential cues to depth and events. (2) How is this information combined by the perceptual system? Viewed in isolation, individual cues typically do not fully specify the environmental properties to which they relate. In general, the rules for projecting three-dimensional layout onto the retina are unambiguously defined, whereas the inverse operation—from the image to the three-dimensional projected scene—is not. (3) Do people perceive space and events accurately? Certainly, people act in the environment as if they represent its spatial relationships accurately; however, effective action can often be achieved without geometrically correct representations. From a pragmatic perspective, perceptual representations are accurate to the degree that they provide effective guidance for behavior. This issue is developed and discussed throughout the chapter. Keywords: binocular disparity; depth cues; ocular-motor depth cues; optical flow; perceptual organization; perspective; spatial layout

One of the reasons we (the authors) enjoy going to live college basketball games is to watch the antics of the student section. We love watching the students’ creativity in trying to pump up the home team and distract the visiting team, especially during free throws. Such escapades made us question whether manipulating what athletes see can influence their subsequent performance. Perception is clearly important for performance. For instance, when athletes look directly at a target without moving their eyes around—a pattern known as the quiet eye—they are more successful in making free throws, putting, and performing a variety of other tasks (e.g., Vickers, 1996, 2007). The quiet eye might lead to more successful performance by focusing attention on targets, and helping athletes to ignore distractors. Additionally, the quiet eye might change the way targets look. Targets presented in the fovea look bigger than those in the periphery (Newsome, 1972), so the quiet eye might lead athletes to perceive targets as bigger. Misperceiving a target as bigger could influence performance in one of three ways. It could disrupt performance because the observer might aim for a location that does not correspond with the target. In this case, the misperception would result in worse performance. However, actions and explicit perceptions may not be influenced by illusions to the same degree (Goodale Milner, 1992). That is, there may be dissociations between perceptions and visually guided actions such that illusions, which fool conscious perception, do not influence subsequent actions (e.g., Ganel, Tanzer, Goodale, 2008). In this case, misperceiving a target as bigger would not affect performance. A final alternative is that misperceiving a target as bigger could enhance performance. Bigger targets feel as if they should be easier to hit, so people may feel more confident when aiming for a bigger target. Given that increased confidence improves performance (e.g., Woodman Hardy, 2003), a perceptually bigger target may also lead to enhanced performance. Here, we report an experiment in which we tested these possibilities.

The logic of judging relative mass from a two-body collision is developed from data presented by Runeson and Vedeler (1993). Data from two experiments are analyzed on a point-by-point basis, and strong support for the theory that mass-ratio judgments are mediated by separate speed and angle heuristics is shown. This analysis is accomplished by reducing the collision event to two elementary features: the presence of ricochet and the ratio of exit speeds. The heuristics that both ricochet and greater exit speed specify relative lightness are shown to explain the basic patterns of data presented by Runeson and Vedeler.

Individuals with autism spectrum disorders (ASDs) have known impairments in social and motor skills. Identifying putative underlying mechanisms of these impairments could lead to improved understanding of the etiology of core social/communicative deficits in ASDs, and identification of novel intervention targets. The ability to perceptually integrate one's physical capacities with one's environment (affordance perception) may be such a mechanism. This ability has been theorized to be impaired in ASDs, but this question has never been directly tested. Crucially, affordance perception has shown to be amenable to learning; thus, if it is implicated in deficits in ASDs, it may be a valuable unexplored intervention target. The present study compared affordance perception in adolescents and adults with ASDs to typically developing (TD) controls. Two groups of individuals (adolescents and adults) with ASDs and age-matched TD controls completed well-established action capability estimation tasks (reachability, graspability, and aperture passability). Their caregivers completed a measure of their lifetime social/communicative deficits. Compared with controls, individuals with ASDs showed unprecedented gross impairments in relating information about their bodies' action capabilities to visual information specifying the environment. The magnitude of these deficits strongly predicted the magnitude of social/communicative impairments in individuals with ASDs. Thus, social/communicative impairments in ASDs may derive, at least in part, from deficits in basic perceptual-motor processes (e.g. action capability estimation). Such deficits may impair the ability to maintain and calibrate the relationship between oneself and one's social and physical environments, and present fruitful, novel, and unexplored target for intervention.

People have a lifetime of experience in which to calibrate their self-produced locomotion with the resultant optical flow. Contrary to walking across the ground, however, walking on a treadmill produces minimal optical flow, and consequentially, a perceptual-motor aftereffect results. We demonstrate that the magnitude of this perceptual-motor aftereffect—measured by forward drift while attempting to march in-place following treadmill walking—decreases as experience walking on a treadmill is acquired over time. Experience with treadmill walking enables walking in this context to become sufficiently distinguished from walking in other contexts. Consequently, two distinct perceptual-motor calibration states are maintained, each linked to the context in which walking occurs. Experience with treadmill walking maintains perceptual-motor calibration accuracy in both walking contexts, despite changes to the relationship between perception and action.

Previous research has shown that hills appear steeper to those who are fatigued, encumbered, of low physical fitness, elderly, or in declining health (Bhalla & Proffitt, 1999; Proffitt, Bhalla, Gossweiler, & Midgett, 1995). The prevailing interpretation of this research is that observers' perceptions of the environment are influenced by their capacity to navigate that environment. The current studies extend this programme by investigating more subtle embodied effects on perception of slant; namely those of mood. In two studies, with two different mood manipulations, and two estimates of slant in each, observers in a sad mood reported hills to be steeper. These results support the role of mood and motivational factors in influencing spatial perception, adding to the previous work showing that energetic potential can influence perception.

This research was designed to test the predictions of 2 approaches to perception. By most traditional accounts, people are thought to derive general-purpose spatial perceptions that are scaled in arbitrary, unspecified units. In contrast, action-specific approaches propose that the angular information inherent in optic flow and ocular-motor adjustments is rescaled and transformed into units related to intended actions. A number of studies have shown, for example, that the apparent distance to targets is scaled by the effort required to walk the extent. Such studies can be accommodated by the traditional account by asserting that the experimental manipulations of walking effort influenced not perception itself, but rather postperceptual response processes. The current studies were designed to assess when and how action-specific influences on distance perception have their effects. The results supported the action-specific account.

The notion that apparent sizes are perceived relative to the size of one’s body is supported through the discovery of a new visual illusion. When graspable objects are magnified by magnifying goggles, they appear to shrink back to near-normal size when one’s hand (also magnified) is placed next to them. When objects are “minified” by minifying goggles, the opposite occurs. The rescaling effect also occurred when participants who were trained in tool use viewed the tool next to the objects. However, this change in apparent size does not occur when familiar objects or someone else’s hand is placed next to the magnified or minified object. Presumably, objects’ apparent sizes shift closer to their actual sizes when one’s hand is viewed because objects’ sizes relative to the hand are the same with or without the goggles. These findings highlight the role of body scaling in size perception.

Durgin et al. (2010) argued that the apparent accuracy of the palmboard measure of geographical slant is accidental and reflects limitations in wrist flexion that reduce palmboard adjustments by just the right amount given the perceptual overestimations upon which they are based. This account is inconsistent with findings that verbal reports and palmboard adjustments are dissociable. In addition to previous evidence found for such dissociation, Durgin et al. also found verbal/palmboard dissociations in Experiment 2. Experiments 1 and 3 of Durgin et al. lacked verbal reports and instead compared palmboard adjustments to free-hand estimates in the context of small wooden surfaces. These experiments are not relevant to the issue of verbal/palmboard dissociability. Across studies, the accuracy of Durgin et al.'s palmboard implementation is far less than that found by others (Feresin & Agostini, 2007). The design of Durgin et al.'s Experiment 5 misrepresented the experimental conditions of Creem and Proffitt (1998), and consequently, the findings of this study have no bearing on the issue at hand.

This study was designed to assess the effects of symmetry and plane of presentation on the determination of the perceptual center of flat figures. Experiment 1 demonstrates the existence of effects in improving center determination, both in the number of sides of the shape and in rotational and reflective symmetry (confounded in the experiment). Experiment 2 shows that the presentation plane has no effect on center determination. In Experiment 3, we divide the effects of the two symmetry types, showing that rotational symmetry alone is as effective as the presence of both symmetry types--that is, the presence of symmetry axes is not very useful in finding perceived centers.

Previous research has demonstrated that changing perceivers' action capabilities can affect their perception of the extent over which an action is performed. In the current study, we manipulated jumping ability by having participants wear ankle weights and examined the influence of this manipulation on the perception of jumpable and un-jumpable extents. When wearing ankle weights, jumpable gaps appeared longer than when not wearing ankle weights; however, for un-jumpable gaps, there was no difference in the apparent gap extent, regardless of whether the participant was wearing ankle weights. This suggests that the perception of a jumpable extent is affected by one's action boundary for jumping, but only if jumping is an action that can be performed over the extent.

Perception of one's body is related not only to the physical appearance of the body, but also to the neural representation of the body. The brain contains many body maps that systematically differ between right- and left-handed people. In general, the cortical representations of the right arm and right hand tend to be of greater area in the left hemisphere than in the right hemisphere for right-handed people, whereas these cortical representations tend to be symmetrical across hemispheres for left-handers. We took advantage of these naturally occurring differences and examined perceived arm length in right- and left-handed people. When looking at each arm and hand individually, right-handed participants perceived their right arms and right hands to be longer than their left arms and left hands, whereas left-handed participants perceived both arms accurately. These experiments reveal a possible relationship between implicit body maps in the brain and conscious perception of the body.

Numerous studies have found that approximately 40% of the adult population behave as if they do not know that water remains horizontal, regardless of the orientation of its container. In the present set of experiments, it was shown that subjects who perform inaccurately do so because they have misrepresented the problem. These individuals are not answering the environment-relative question, “What should the water's surface orientation be relative to the environment?” Instead, they attempt to solve an object-relative problem, “How should water incline relative to its tilted container?” It was shown that subjects' problem representations can be influenced by manipulating the manner in which the problem is presented, and that performance is affected accordingly. Experiment 1 was a pretest, designed primarily to identify individuals who perform correctly or incorrectly on the traditional paper-and-pencil task. Experiment 1 also demonstrated that by promoting an object-relative perspective, a majority of subjects can be induced into performing incorrectly on the water level problem. Experiment 2 found that when individuals were led to evaluate the problem from an environment-relative perspective, they performed accurately, regardless of their performance in Experiment 1. Experiment 3 found that subjects who performed incorrectly on the paper-and-pencil problem are not simply more variable than those who are accurate, but rather that the object-relative perspective creates a bias toward drawing liquid surface orientations that incline in the same direction as the tilt of the container. Experiment 4 found that the response bias observed in Experiment 3 is the result of a frame of reference perceptual influence. The orientation of the surrounding container affects the apparent tilt of the liquid surface. In summary, it was shown that people fail on the water level problem, not because they are lacking the relevant knowledge, but rather because they are attempting to solve a different problem—a problem represented in an objectrelative, as opposed to an environment-relative coordinate system. Moreover, object-relative solutions manifest a perceptual bias that is inherent in all people.

The visual perception of geographical slant is influenced by physiological resources, such as physical fitness, age, and being physically refreshed. In two studies we tested whether a psychosocial resource, social support, can also affect the visual perception of slants. Participants accompanied by a friend estimated a hill to be less steep when compared to participants who were alone (Study 1). Similarly, participants who thought of a supportive friend during an imagery task saw a hill as less steep than participants who either thought of a neutral person or a disliked person (Study 2). In both studies, the effects of social relationships on visual perception appear to be mediated by relationship quality (i.e., relationship duration, interpersonal closeness, warmth). Artifacts such as mood, social desirability, and social facilitation did not account for these effects. This research demonstrates that an interpersonal phenomenon, social support, can influence visual perception.

There is an increasing need for methods for secure dissemination of interactive 3D graphics content, providing protection for valuable 3D models while still allowing them to be widely shared. Existing systems for protected sharing of 3D models may introduce perturbations into the rendered images of the content, in order to defend against potential malicious reconstruction attacks that could otherwise recover the 3D model shape. However, the particular nature and magnitude of these perturbation defenses has not been based upon any rigorous analysis or measurement of their perceptual effect on non-malicious users of the protected graphics system. In this paper, we take the first steps toward such an analysis, conducting a series of user studies that evaluate the impact (as measured by user reaction time) of varying amounts of noise applied to user interactions in a real-time 3D rendering system. We are thus able to experimentally determine the most appropriate tradeoffs between noise perturbation defenses and the security of the 3D content against typical reconstruction attacks.

When people are engaged in a skilled behavior, such as occurs in sports, their perceptions relate optical information to their performance. In the present research, we demonstrate the effects of performance on size perception in golfers. We found that golfers who played better judged the hole to be bigger than did golfers who did not play as well. In follow-up laboratory experiments, participants putted on a golf mat from a location near or far from the hole and then judged the size of the hole. Participants who putted from the near location perceived the hole to be bigger than did participants who putted from the far location. Our results demonstrate that perception is influenced by the perceiver's current ability to act effectively in the environment.

Emotion and psychopathology researchers have described the fear response as consisting of four main components – subjective affect, physiology, cognition, and behavior. The current study provides evidence for an additional component in the domain of height fear - perception - and shows that it is distinct from measures of cognitive processing. Individuals High (N = 35) and Low (N = 36) in acrophobic symptoms looked over a two-story balcony ledge and estimated its vertical extent using a direct height estimation task (visual matching), and an indirect task (size estimation); the latter task seems to exhibit little influence from cognitive factors. In addition, implicit and explicit measures of cognitive processing were obtained. Results indicated that, as expected, the High Fear group showed greater relative, implicit height fear associations and explicit threat cognitions. Of primary interest, the High (compared to Low) Fear group estimated the vertical extent to be higher, and judged target sizes to be greater, even when controlling for the cognitive bias measures. These results suggest that emotional factors such as fear are related to perception.

It is commonly assumed that perceived distance in full-cue, ecologically valid environments is redundantly specified and approximately veridical. However, recent research has called this assumption into question by demonstrating that distance perception varies in different types of environments even under full-cue viewing conditions. We report five experiments that demonstrate an effect of environmental context on perceived distance. We measured perceived distance in two types of environments (indoors and outdoors) with two types of measures (perceptual matching and blindwalking). We found effects of environmental context for both egocentric and exocentric distances. Across conditions, within individual experiments, all viewer-to-target depth-related variables were kept constant. The differences in perceived distance must therefore be explained by variations in the space beyond the target.

Perceived slant is grossly overestimated, such that 5° hills look to be about 20°. However, overestimation is found only in visual and verbal measures of apparent slant; action measures are accurate. This dissociation is consistent with several lines of research that suggest that there exist two perceptual processes, one for visually guided actions and another for explicit awareness. However, studies in other contexts have shown that analogous effects can be the result of differences in the task demands associated with the responses themselves as opposed to the processes underlying the responses. Two experiments are reported in which these alternatives were tested. Our results are consistent with the hypothesis that two perceptual processes underlie the dissociation between explicit awareness and visuomotor assessments of perceived slant.

This paper explores the validation of tactile mechanisms as an effective means of communications for integration into a physiologic system interface (PSI). Tactile communications can offer a channel that only minimally interferes with a primary or concurrent task. The PSI will use functional brain imaging techniques, specifically functional near-infrared imaging (fNIR), to determine cognitive workload in language and visual processing areas of the brain. The resulting closed-loop system will thus have the capability of providing the operator with necessary information by using the modality most available to the user, thus enabling effective multi-tasking and minimal task interference.

This paper discusses two functional brain imaging techniques, functional magnetic resonance imaging (fMRI) and functional near-infrared (fNIR) imaging, and their applications for quantitative usability analysis. This application is demonstrated through a two-phase study on reading effort required for varying degrees of font degradation. The first phase used fMRI to map cortical locations that were active while subjects read fonts of varying quality. The second phase used fNIR imaging, which showed higher levels of activity (and thus greater cognitive effort) in the visual processing area of the brain during a reading task with text presented in degraded fonts. The readability analysis techniques demonstrated in this study also generalize to applications requiring an objective analysis of interface usability.

Functional near-infrared sensing (fNIR) enables real-time, non-invasive monitoring of cognitive activity by measuring the brain's hemodynamic and metabolic responses. We have demonstrated the ability for non-vocal and non-physical communications through detecting directed changes in cognitive tasks. Building upon past research, this paper reports methods that allow the calibration of the fNIR oxygenation signal to better be used in more complex communicative and selection tasks. This work is then discussed in the context of a faster, continuous fNIR brain-computer interface framework.

Previous research has found performance for several egocentric tasks to be superior on physically large displays relative to smaller ones, even when visual angle is held constant. This finding is believed to be due to the more immersive nature of large displays. In our experiment, we examined if using a large display to learn a virtual environment (VE) would improve egocentric knowledge of the target locations. Participants learned the location of five targets by freely exploring a desktop large-scale VE of a city on either a small (25" diagonally) or large (72" diagonally) screen. Viewing distance was adjusted so that both displays subtended the same viewing angle. Knowledge of the environment was then assessed using a head-mounted display in virtual reality, by asking participants to stand at each target and paint at the other unseen targets. Angular pointing error was significantly lower when the environment was learned on a 72" display. Our results suggest that large displays are superior for learning a virtual environment and the advantages of learning an environment on a large display may transfer to navigation in the real world.

When walking effort is increased due to manipulations such as wearing heavy backpacks, people perceive hills to be steeper and distances to be farther (Bhalla & Proffitt, 1999; Proffitt, Stefanucci, Banton, & Epstein, 2003). On the basis of these findings, we expected people to overestimate distances on steep hills relative to the same distances on flat ground, because of the increased effort required to ascend or descend them. This hypothesis is in contrast to the belief that distances are specified solely by optical and oculomotor information related to the geometry of the environment. To test the hypothesis, we investigated distance estimation on hills and flat terrains in natural and virtual environments. We found that participants judged steep uphill and downhill distances to be farther than the same distances on flat terrain. These results are inconsistent with the idea that spatial layout is perceived solely in terms of geometry, lending partial support to an effort hypothesis.

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.

Perceiving egocentric distance is not only a function of the optical variables to which it relates, but also a function of people's current physiological potential to perform intended actions. In a set of experiments, we showed that, as the effort associated with walking increases, perceived distance increases if the perceiver intends to walk the extent, but not if the perceiver intends to throw. Conversely, as the effort associated with throwing increases, perceived distance increases if people intend to throw to the target, but not if they intend to walk. Perceiving distance combines the geometry of the world with our behavior goals and the potential of our body to achieve these goals.

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 self-position. 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.

We are interestind in building and evaluating human computer interfaces that make information more memorable. Psychology research informs us that humans access memories through cues, or "memory hooks," acquired at the time we learn the information. In this paper, we show that kinesthetic cues, or the awareness of parts of our body's position with respect to itself or to the environment, are useful for recalling the positions of objects in space. We report a user study demonstrating a 19% increase in spatial memory for information controlled with a touchscreen, which provides direct kinesthetic cues, as compared to a standard mouse interface. We also report results indicating that females may benefit more than males from using the touchscreen device.