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Abstracts

Weser, V., Finotti, G., Costantini, M., & Proffitt, D.R. (2017). Multisensory integration induces body ownership of a handtool, but not any handtool. Consciousness and Cognition 56

Bodily boundaries are computed by integrating multisensory bodily signals and can be experimentally manipulated using bodily illusions. Research on tool use demonstrates that tools alter body representations motorically to account for changes in a user’s action repertoire. The present experiment sought to unify perceptual and motoric accounts of tool embodiment using a modified Rubber Hand Illusion (RHI) that also addressed the skill and practice aspects of the tool use literature. In Experiment 1, synchronous multisensory stimulation induced perceptual embodiment of a tool, chopsticks. The embodiment of chopsticks was stronger for more skilled participants, and if the illusion was preceded by tool use. In Experiment 2, the illusion was not elicited with a different type of tool, a teacup, showing that not all objects can be incorporated. This experiment helps to clarify the role of perceptual and motoric embodiment and suggests future avenues for research into tools embodiment using this method.

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Zadra, J.R., Weltman, A.L., & Proffitt, D.R. (2015). Walkable Distances Are Bioenergetically Scaled. Journal of Experimental Psychology: Human Perception and Performance. Advance online publication.

In perceiving spatial layout, the angular units of visual information are transformed into linear units appropriate for specifying size and extent. This derivation of linear units from angular ones requires geometry and a ruler. Numerous studies suggest that the requisite perceptual rulers are derived from the observer’s body. In the case of walkable extents, it has been proposed that people scale distances to the bioenergetic resources required to traverse the extents relative to the bioenergetic resources currently available. The current study sought to rigorously test this proposal. Using methods from exercise physiology, a host of physiological measures were recorded as participants engaged in exercise on 2 occasions: once while provided with a carbohydrate supplement and once with a placebo. Distance estimates were made before and after exercise on both occasions. As in previous studies, the carbohydrate manipulation caused decreased distance estimates relative to the placebo condition. More importantly, individual differences in physiological measures that are associated with physical fitness predicted distance estimates both before and after the experimental manipulations. Results suggest that walkable distances are bioenergetically scaled.

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Twedt, E. & Proffitt, D. R. (2013). Perception. In D. S. Dunn (Ed.), Oxford Bibliographies in Psychology. New York: Oxford University Press.

No abstract available now.

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Proffitt, D.R. and Linkenauger, S. A. (2013). Perception viewed as a phenotypic expression. In W. Prinz, M. Beisert, & A. Herwig (Eds.), Tutorials In Action Science, MIT Press.

No abstract available now.

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Proffitt, D.R. (2013). An embodied approach to perception: By what units are Visual perceptions scaled? Perspectives on Psychological Science, 8, 474-483.

When humans perceive the environment, angular units of visual information must be transformed into units appropriate for the specification of such parameters of surface layout as extent, size, and orientation. Our embodied approach to perception proposes that these scaling units derive from the body. For example, hand size is relevant for scaling the size of a strawberry, whereas an extent across a meadow is scaled by the amount of walking required to traverse it. In his article, Firestone (2013, this issue) argued that our approach is wrong; in fact, he argued that it must be wrong. This reply to Firestone’s critique is organized into three parts, which address the following questions: (a) What is the fundamental question motivating our approach? (b) How does our approach answer this question? (c) How can we address Firestone’s arguments against our approach? A point-by-point critique of Firestone’s arguments is presented. Three conclusions are drawn: (a) Most of Firestone’s arguments reflect a misunderstanding of our approach, (b) none of his arguments are the fatal flaws in our approach that he believes them to be, and (c) there are good reasons to believe that perception—just like any other biological function—is a phenotypic expression.

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Gross, E.B. & Proffitt, D.R. (2013). The economy of social resources and its influence on social perceptions. Frontiers in Human Neuroscience 7:772.

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.

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Witt, J. K., Linkenauger, S. A., & Proffitt, D. R. (2012). Get Me Out of This Slump! Visual Illusions Improve Sports Performance. Psychological Science, 19-21. doi:10.1177/0956797611428810

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.

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Linkenauger, S. A., Lerner, M. D., Ramenzoni, V. C., & Proffitt, D. R. (2012). A Perceptual–Motor Deficit Predicts Social and Communicative Impairments in Individuals With Autism Spectrum Disorders. Autism Research, 5, 352-362.

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.

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Zadra, J. R., & Clore, G. L. (2011). Emotion and perception: the role of affective information. Wiley Interdisciplinary Reviews: Cognitive Science, 2(6), 676-685. John Wiley & Sons, Inc. doi:10.1002/wcs.147

Visual perception and emotion are traditionally considered separate domains of study. In this article, however, we review research showing them to be less separable than usually assumed. In fact, emotions routinely affect how and what we see. Fear, for example, can affect low-level visual processes, sad moods can alter susceptibility to visual illusions, and goal-directed desires can change the apparent size of goal-relevant objects. In addition, the layout of the physical environment, including the apparent steepness of a hill and the distance to the ground from a balcony can both be affected by emotional states. We propose that emotions provide embodied information about the costs and benefits of anticipated action, information that can be used automatically and immediately, circumventing the need for cogitating on the possible consequences of potential actions. Emotions thus provide a strong motivating influence on how the environment is perceived.

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Riener, C. R., Stefanucci, J. K., Proffitt, D. R., & Clore, G. (2011). An effect of mood on the perception of geographical slant. Cognition & emotion, 25(1), 174-82. doi:10.1080/02699931003738026

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.

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Linkenauger, S. A., Witt, J. K., and Proffitt, D. R. (2011). Taking a hands-on approach: Apparent grasping ability scales the perception of object size. Journal of Experimental Psychology: Human Perception and Performance, 37(5) 1432-1441.

We examined whether the apparent size of an object is scaled to the morphology of the relevant body part with which one intends to act on it. To be specific, we tested if the visually perceived size of graspable objects is scaled to the extent of apparent grasping ability for the individual. Previous research has shown that right-handed individuals perceive their right hand as larger and capable of grasping larger objects than their left. In the first 2 experiments, we found that objects looked smaller when placed in or judged relative to their right hand compared to their left. In the third experiment, we directly manipulated apparent hand size by magnifying the participants’ hands. Participants perceived objects to be smaller when their hand was magnified than when their hand was unmagnified. We interpret these results as demonstrating that perceivers use the extent of their hands’ grasping abilities as “perceptual rulers” to scale the apparent size of graspable objects. Furthermore, hand size manipulations did not affect the perceived size of objects too big to be grasped, which suggests that hand size is only used as a scaling mechanism when the object affords the relevant action, in this case, grasping.

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Linkenauger, S. A., Mohler, B. J., Proffitt, D. R. (2011). Body-based perceptual rescaling revealed through the size - weight illusion. Perception, 40, 1251-1253.

An embodied approach to the perception of spatial layout contends that the body is used as a `perceptual ruler' with which individuals scale the perceived environmental layout. In support of this notion, previous research has shown that the perceived size of objects can be influenced by changes in the apparent size of hand. The size ^ weight illusion is a well known phenomenon, which occurs when people lift two objects of equal weight but differing sizes and perceive that the larger object feels lighter. Therefore, if apparent hand size influences perceived object size, it should also influence the object's perceived weight. In this study, we investigated this possibility by using perceived weight as a measure and found that changes in the apparent size of the hand influence objects' perceived weight.

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Lee C, Linkenauger SA, Bakdash JZ, Joy-Gaba JA, Profitt DR (2011) Putting Like a Pro: The Role of Positive Contagion in Golf Performance and Perception. PLoS ONE 6(10): e26016. doi:10.1371/journal.pone.0026016

Many amateur athletes believe that using a professional athlete’s equipment can improve their performance. Such equipment can be said to be affected with positive contagion, which refers to the belief of transference of beneficial properties between animate persons/objects to previously neutral objects. In this experiment, positive contagion was induced by telling participants in one group that a putter previously belonged to a professional golfer. The effect of positive contagion was examined for perception and performance in a golf putting task. Individuals who believed they were using the professional golfer’s putter perceived the size of the golf hole to be larger than golfers without such a belief and also had better performance, sinking more putts. These results provide empirical support for anecdotes, which allege that using objects with positive contagion can improve performance, and further suggest perception can be modulated by positive contagion.

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Witt, J. K., Proffitt, D. R., & Epstein, W. (2010). When and how are spatial perceptions scaled? Journal of Experimental Psychology: Human Perception and Performance, 36(5), 1153-1160. doi: 10.1037/a0019947.

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved).

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Schnall, S., Zadra, J. R., & Proffitt, D. R. (2010). Direct evidence for the economy of action: Glucose and the perception of geographical slant. Perception, 39(4), 464-482. doi: 10.1068/p6445.

When locomoting in a physically challenging environment, the body draws upon available energy reserves to accommodate increased metabolic demand. Ingested glucose supplements the body’s energy resources, whereas non-caloric sweetener does not. Two experiments demonstrate that participants who had consumed a glucose-containing drink perceived the slant of a hill to be less steep than did participants who had consumed a drink containing non-caloric sweetener. The glucose manipulation influenced participants’ explicit awareness of hill slant but, as predicted, it did not affect a visually guided action of orienting a tilting palmboard to be parallel to the hill. Measured individual differences in factors related to bioenergetic state, such as fatigue, sleep quality, fitness, mood, and stress, also affected perception: lower energetic states were associated with steeper perceptions of hill slant. This research shows that the perception of the spatial layout of the environment is influenced by the energetic resources available for locomotion within it. Our findings are consistent with the view that spatial perceptions are influenced by bioenergetic factors.

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Proffitt, D. R., & Zadra, J. R. (2010). Explicit and motoric dependent measures of geographical slant are dissociable: A reassessment of the findings of Durgin, Hajnal, Li, Tonge, and Stigliani (2010). Acta psychologica, 4-7. Elsevier B.V. doi:10.1016/j.actpsy.2010.06.003

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.

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Linkenauger, S. A., Ramenzoni, V., & Proffitt, D. R. (2010). Illusory shrinkage and growth: body-based rescaling affects the perception of size. Psychological Science, 21(9), 1318-25. doi: 10.1177/0956797610380700.

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.

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Stefanucci, J. K., & Proffitt, D. R. (2009). The roles of altitude and fear in the perception of height. Journal of experimental psychology. Human perception and performance, 35(2), 424-38. doi: 10.1037/a0013894.

Previous research on perceiving spatial layout has found that people often exhibit normative biases in their perception of the environment. For instance, slant is typically overestimated and distance is usually underestimated. Surprisingly, however, the perception of height has rarely been studied. The present experiments examined the perception of height when viewed from the top (e.g., looking down), or from the bottom (e.g., looking up). Multiple measures were adapted from previous studies of horizontal extents to assess the perception of height. Across all of the measures, a large, consistent bias was found: vertical distances were greatly overestimated, especially from the top. Secondary findings suggest that the overestimation of distance and size that occurs when looking down from a high place correlates with reports of trait- and state-level fear of heights, suggesting that height overestimation may be due, in part, to fear.

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Proffitt, D. R. (2009). Affordances matter in geographical slant perception. Psychonomic bulletin & review, 16(5), 970-2. doi: 10.3758/PBR.16.5.970.

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.

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Linkenauger, S. a, Witt, J. K., Stefanucci, J. K., Bakdash, J. Z., & Proffitt, D. R. (2009). The effects of handedness and reachability on perceived distance. Journal of experimental psychology. Human perception and performance, 35(6), 1649-60. doi: 10.1037/a0016875.

Previous research has suggested that perceived distances are scaled by the action capabilities of the body. The present studies showed that when reachability is constrained due to a difficult grasp to pick up an object, perceived distance to the object increases. Participants estimated the distances to tools whose orientations made them either easy or difficult to grasp with their dominant and non-dominant hands. Right-handed participants perceived tools that were more difficult to grasp to be farther away than tools that were easier to grasp. However, perceived distance did not differ in left-handed participants. These studies suggest that when reaching to a target, the distance to that target is scaled in terms of how far one can effectively reach given the type of reaching posture that is executed. Furthermore, this effect is modulated by handedness.

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Linkenauger, S. A., Witt, J. K., Bakdash, J. Z., Stefanucci, J. K., & Proffitt, D. R. (2009). Asymmetrical body perception: A possible role for neural body representations. Psychological Science, 20(11), 1373.

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.

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Lessard, D. A., Linkenauger, S. A., & Proffitt, D. R. (2009). Look before you leap: Jumping ability affects distance perception. Perception, 38(12), 1863-1866. doi: 10.1068/p6509.

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 influ- ence 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

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Clerkin, E. M., Cody, M. W., Stefanucci, J. K., Proffitt, D. R., & Teachman, B. A.(2009). Imagery and fear influence height perception. Journal of Anxiety Disorders, 23, 381-386.

The current study tested whether height overestimation is related to height fear and influenced by images of falling. To assess perceptual biases, participants high (n=65) versus low (n=64) in height fear estimated the vertical extents of two balconies using a visual matching task. On one of the balconies, participants engaged in an imagery exercise designed to enhance the subjective sense that they were acting in a dangerous environment by picturing themselves falling. As expected, we found that individuals overestimated the balcony's height more after they imagined themselves falling, particularly if they were already afraid of heights. These findings suggest that height fear may serve as a vulnerability factor that leads to perceptual biases when triggered by a stressor (in this case, images of falling).

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Zhu, J., Bakdash, J.Z., Koller, D., Banton, T.B., Proffitt, D.R., and Humpherys, G. (2008). Quantifying Usability in Secure Graphics: Assessing the user costs of protecting 3-D content. In Proceedings of the 5th Annual ACM SIGGRAPH Symposium on Applied Perception in Graphics and Visualization.

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.

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Witt, J.K., Linkenauger, S.A., Bakdash, J.Z., Proffitt, D.R. (2008) Putting to a bigger hole: Golf performance relates to perceived size. Psychonomic Bulletin and Review, 15(3).

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.

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Witt, J., Linkenauger, S., Bakdash, J., Augustyn, J., Cook, A., & Proffitt, D. (2008). The long road of pain: chronic pain increases perceived distance. Experimental Brain Research.

Spatial perception is sensitive to the energetic costs required to perform intended actions. For example, hills look steeper to people who are fatigued or burdened by a heavy load. Similarly, perceived distance is also influenced by the energy required to walk or throw to a target. Such experiments demonstrate that perception is a function, not just of optical information, but also of the perceiver’s potential to act and the energetic costs associated with the intended action. In the current paper, we expand on the notion of “cost” by examining perceived distance in patients diagnosed with chronic pain, a multifactorial disease, which is experienced while walking. We found that chronic pain patients perceive target distances to be farther away compared with a control group. These results indicate the physical, and perhaps emotional, costs of chronic pain affect spatial perceptions.

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Witt, J. K., & Proffitt, D. R. (2008). Action-specific influences on distance perception: a role for motor simulation. Journal of experimental psychology. Human perception and performance, 34(6), 1479-92. doi: 10.1037/a0010781.

Perception is influenced by the perceiver’s ability to perform intended actions. For example, when people intend to reach with a tool to targets that are just beyond arm’s reach, the targets look closer than when they intend to reach without the tool (Witt, Proffitt, & Epstein, 2005). This is one of several examples demonstrating that behavioral potential affects perception. However, the action-specific processes that are involved in relating the person’s abilities to perception have yet to be explored. Four experiments are presented that implicate motor simulation as a mediator of these effects. When a perceiver intends to perform an action, the perceiver runs a motor simulation of that action. The perceiver’s ability to perform the action, as determined by the outcome of the simulation, influences perceived distance.

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Teachman, B. A., Stefanucci, J. K., Clerkin, E. M., Cody, M. W., & Proffitt, D. R. (2008). A new mode of fear expression: Perceptual bias in height fear. Emotion, 8, 296-301.

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.

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Stefanucci, J. K., Proffitt, D. R., Clore, G., & Parekh, N. (2008). Skating down a steeper slope: Fear influences the perception of geographical slant. Perception, 37, 321-323.

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.

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Schnall, S., Harber, K. D., Stefanucci, J. K., & Proffitt, D. R. (2008). Social support and the perception of geographical slant. Journal of Experimental Social Psychology, 44, 1246-1255.

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.

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Proffitt, D. R. (2008). An Action Specific Approach to Spatial Perception. In R. L. Klatzky, B. MacWhinney & M. Behrmann (Eds.), Embodiment, Ego-Space, and Action. New York: Psychology Press.

No abstract available now.

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Bakdash, J.Z., Linkenauger, S.A., and, Proffitt, D.R. (2008). Comparing decision-making vs. control for learning a virtual environment: Backseat drivers learn where they are going. In Human Factors and Ergonomics Society 2008 Conference Proceedings.

A considerable amount of research has been conducted on the role interactivity, active versus passive navigation, for learning the spatial layout of a virtual environment (VE). However, active navigation is not unitary. It has two distinct components: decision-making and control. In the present work we investigated which main component of active navigation was critical for acquiring spatial knowledge of a virtual city. We found that spatial knowledge was comparable when the VE was learned with active navigation or decision-making in the absence of control, but was much worse when only control was present. These results suggest decision-making, not control, is the critical component for learning a VE.

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Witt, J.K., & Proffitt, D.R. (2007). Perceived slant: A dissociation between perception and action. Perception, 36, 249-257.

Perceived slant is grossly overestimated such that 5° hills look to be about 20°. However, overestimation is only found 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 2 perceptual processes, one for visually-guided actions and another for explicit awareness. However, studies in other contexts have shown that analogous effects can be due to differences in the task demands associated with the responses themselves as opposed to the processes underlying the responses. The following experiments directly test these 2 alternatives. Our results are consistent with the hypothesis that 2 perceptual processes underlie the dissociation between explicit awareness and visuomotor assessments of perceived slant.

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Witt, J. K., Stefanucci, J. K., Riener, C. R., & Proffitt, D. R. (2007). Seeing beyond the target: An effect of environmental context on distance perception. Perception, 36, 1752-1768.

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.

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Stefanucci, J. K., O’Hargan, S. P., & Proffitt, D. R. (2007). Augmenting context-dependent memory. Journal of Cognitive Engineering and Decision Making, 1, 391-404.

The goal of this study was to design a human-computer interface that would increase the memorability of information presented by providing context as compared with memory with no context. Our focus was in augmenting context-dependent mem- ory because it is a powerful and often unexploited characteristic of human cognition. To amplify this cognitive strength, we built the InfoCockpit, which included a large screen containing projected images of places, a three-dimensional surround-sound system that played ambient noises congruent with the projected images, and a flat-panel monitor that served as the focal display for the presentation of the to-be-remembered information. Participants in our study learned and recalled information in either the InfoCockpit or a standard desktop environment. The InfoCockpit group demonstrated a 131% memory advantage. Contextual factors that were previously found to be effective in isolation created a large effect when presented in combination.

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Proffitt, D.R., Stefanucci, J., Banton, T., & Epstein, W. (2007). Reply to Hutchison and Loomis. The Spanish Journal of Psychology. 9, 340-342.

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.

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Proffitt, D.R., Stefanucci, J., Banton, T., & Epstein, W. (2007). A Final Reply to Hutchison and Loomis. The Spanish Journal of Psychology, 9, 346-348.

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.

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Proffitt, D.R. (2006). Embodied perception and the economy of action. Perspectives on Psychological Science, 1(2), 110-122.

Perception informs people about the opportunities for action and their associated costs. To this end, explicit awareness of spatial layout varies not only with relevant optical and ocular-motor variables, but also as a function of the costs associated with performing intended actions. Although explicit awareness is mutable in this respect, visually guided actions directed at the immediate environment are not. When the metabolic costs associated with walking an extent increase—perhaps because one is wearing a heavy backpack—hills appear steeper and distances to targets appear greater. When one is standing on a high balcony, the apparent distance to the ground is correlated with one’s fear of falling. Perceiving spatial layout combines the geometry of the world with behavioral goals and the costs associated with achieving these goals.

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Proffitt, D.R. (2006). Distance perception. Current Directions in Psychological Research, 15, 131-135.

Distance perception seems to be an incredible achievement if it is construed as being based solely on static retinal images. Information provided by such images is sparse at best. On the other hand, when the perceptual context is taken to be one in which people are acting in natural environments, the informational bases for distance perception become abundant. There are, however, surprising consequences of studying people in action. Nonvisual factors, such as people’s goals and physiological states, also influence their distance perceptions. Although the informational specification of distance becomes redundant when people are active, paradoxically, many distance-related actions sidestep the need to perceive distance at all.

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Bakdash, J. Z., Augustyn, J. S., and Proffitt, D. R. (2006). Large displays enhance spatial knowledge of a virtual environment. In ACM Siggraph Symposium on Applied Perception in Graphics and Visualization, 59-62.

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 point 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.

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Witt, J.K., Proffitt, D.R., & Epstein, W. (2005). Tool use affects perceived distance but only when you intend to use it. Journal of Experimental Psychology: Human Perception and Performance, 31, 880-888.

Recent research demonstrates neurological and behavioral differences in people's responses to the space that is within and beyond reach. The current studies demonstrated a perceptual difference as well. Reachability was manipulated by having participants reach with and without a tool. Across two conditions, in which participants either held a tool or not, targets were presented at the same distances. Perceived distances to targets within reach holding the tool were compressed compared to targets that were beyond reach without it. These results suggest that reachability serves as a metric for perception. The third experiment found that reachability only influenced perceived distance when the perceiver intended to reach. These experiments suggest that we perceive the environment in terms of our intentions and abilities to act within it.

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Witt, J.K., & Proffitt, D.R. (2005). See the ball, hit the ball: Apparent ball size is correlated with batting average. Psychological Science, 16(12), 937-938.

Baseball players frequently say that the ball appears bigger when they are hitting well. In describing a mammoth 565ft home run, Mickey Mantle said, “I never really could explain it. I just saw the ball as big as a grapefruit” (Ultimate New York Yankees, n.d.). George Scott of the Boston Red Sox said, “When you’re hitting the ball [well], it comes at you looking like a grapefruit. When you’re not, it looks like a blackeyed pea” (Baseball Almanac, n.d.). During a slump, Joe “Ducky” Medwick of the St. Louis Cardinals said he felt like he was “swinging at aspirins” (ESPNMAG.com, n.d.). Similar comments have been made by such Hall of Famers as Ted Williams (Roger Joslin, n.d.), “Wee” Willie Keeler (ESPNMAG.com, n.d.), George Brett (LA Article, n.d.), and more. This phenomenon is not limited to baseball. When playing well, tennis players report that the ball looks huge, golfers say the cup looks bigger, and basketball players say the hoop looks enormous. All of these people report perceptions, which were modulated by performance efficacy. Our experiment confirms that this phenomenon is a psychological reality.

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Stefanucci, J., Proffitt, D., Banton, T., & Epstein, W. (2005). Distances appear different on hills. Perception & Psychophysics, 67(6), 1052-1060.

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.

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Riener, C. R., Proffitt, D., & Salthouse, T. (2005). A psychometric approach to intuitive physics. Psychonomic Bulletin and Review, 12(4), 740-746.

The literature on intuitive physics shows that many people exhibit systematic errors when predicting the behavior of simple physical events. Most previous research has attributed these errors to factors specific to a certain class of tasks. In the present study, we investigated the possibility that intuitive physics performance may be related to general measures of cognitive ability. Two hundred four adults (ages, 20–91 years) were presented with five pairs of intuitive physics questions. It was found that performance on the intuitive physics items was moderately intercorrelated, suggesting that they were tapping into a unitary construct. Despite the correlation with factors that decline with advancing age, intuitive physics performance was not correlated with age (r = .00). The findings are discussed in the context of research on intuitive physics, as well as research on cognitive aging.

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Banton, T., Stefanucci, J., Durgin, J., Fass, A., & Proffitt, D. (2005). The Perception of Walking Speed in a Virtual Environment. Presence, 14(4), 394-406.

Studies of locomotion in virtual environments assume that correct geometric principles define the relationship between walking speed and environmental flow. However, we have observed that geometrically correct optic flow appears to be too slow during simulated locomotion on a treadmill. Experiment 1 documents the effect in a head-mounted display. Experiment 2 shows that the effect is eliminated when the gaze is directed downward or to the side, or when the walking speed is slow. Experiment 3 shows that the effect is unchanged by stride length. Experiment 4 verifies that the effect is not attributable to image jitter. The change in perceived speed from straight ahead to side or down gaze coincides with a shift from expanding optic flow to lamellar flow. Therefore, we hypothesize that lamellar flow is necessary for accurate speed perception, and that a limited field of view eliminates this cue during straight-ahead gaze.

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Witt, J.K., Proffitt, D.R., & Epstein, W. (2004). Perceiving distance: A role of effort and intent. Perception, 33, 570-590.

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.

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Proffitt, D.R., Stefanucci, J., Banton, T., & Epstein, W. (2003). The role of effort in perceiving distance. Psychological Science.

Berkeley (1709) proposed that space is perceived in terms of effort. Consistent with his proposal, we found that egocentric distances appear greater when people are encumbered due to their wearing a heavy backpack or following a visual-motor adaptation that reduces the anticipated optic flow coinciding with walking effort. In accord with Berkeley’s proposal and Gibson’s theory of affordances, these studies show that the perception of spatial layout is influenced by locomotor effort.

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Tan, D.S., Stefanucci, J.K., Proffitt, D.R., Pausch, R. (2002). Kinesthesis Aids Human Memory. Short paper at CHI 2002 Conference on Human Factors in Computing Systems, Minneapolis, MN.

We are interested 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.

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Stefanucci, J. K., Downs, T. H., Snyder, A. P., Downs, J. H., Proffitt, D.R. (2002). Context-dependent memory engages a frontal-parietal-occipital network. Poster presented at the Annual Meeting of the Cognitive Neuroscience Society, San Francisco, CA.

No abstract available now.

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Stefanucci, J. K., & Proffitt, D. R. (2002). Providing distinctive cues to augment human memory. Poster presented at the 24th Annual meeting of the Cognitive Science Society, Fairfax, VA.

Previous research in our lab (Tan, Stefanucci, Proffitt & Pausch, 2001) demonstrated that a multimodal prototype computer system, the InfoCockpit, could increase users’ memory of information compared to a standard desktop computer. Displaying information on multiple monitors with ambient visual and auditory dispays engages context-dependent memory and memory for location, thus facilitating recall. We replicate this finding and isolate the memory cues to find whether the combination of contextual information and spatial location is necessary to obtain this memory advantage. Our findings show that contextual information alone provides users with the best strategy for later recall.

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Riener, C., Proffitt, D., & Salthouse, T. (2002, March) Intuitive Physics: Across Tasks and Age. Poster session presented at the annual University of Virginia Graduate Research Fair, Charlottesville, Virginia.

No abstract available now.

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Riener, C., Proffitt, D ., & Salthouse, T. (2002, April) Intuitive physics: Across tasks and age. Poster presented at the bi-annual meeting of the Cognitive Aging Conference, Atlanta, Georgia.

No abstract available now.

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Riener, C. & Proffitt, D. (2002). Quantifying spatial presence. Fifth Annual International Workshop on Presence (pp. 345-352).

No abstract available now.

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Proffitt, D. R. & Caudek, C. (2002). Depth perception and perception of events. In A. F. Healy and R. W. Proctor (Eds.). Comprehensive handbook of psychology, volume 4: Experimental psychology. NY: Wiley.

This chapter begins by reviewing the literature that addresses 2 questions: What is the information provided for perceiving spatial relationships and how is this information combined by the perceptual system? The authors then address a third question: Do people perceive spatial layout accurately? The answer to this question depends upon the criteria used to define accuracy. Certainly, people act in the environment as if they represent its spatial relationships accurately; however, effective action can often be achieved without this accurate representation. This issue is developed and discussed throughout this chapter.

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Dixon, M. W. & Proffitt, D. R. (2002). Overestimation of heights in virtual reality is influenced more by perceived distal size than by the 2-D versus 3-D dimensionality of the display. Perception, 31, 103-112.

One important aspect of the pictorial representation of a scene is the depiction of object proportions. Yang, Dixon, and Proffitt (1999 Perception 28 445-467) recently reported that the magnitude of the vertical-horizontal illusion was greater for vertical extents presented in three-dimensional (3-D) environments were large and all of the 2-D displays were small, the question remains whether the observed magnitude differences were due solely to the dimensionality of the displays (2-D versus 3-D) or to the perceived distal size of the extents (small versus large). We investigated this question by comparing observers judgments of vertical relative to horizontal extents on a large but 2-D display compared to the large 3-D and the small 2-D displays used by Yang et al (1999). The results confirmed that the magnitiude differences for vertical overestimation between display media are influenced more by the perceived distal object size rather than by the dimensionality of the display.

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Tan, D.S., Stefanucci, J.K., Proffitt, D.R., Pausch, R. (2001) The Infocockpit: Providing Location and Place to Aid Human Memory. Workshop on Perceptive User Interfaces 2001, Orlando, Florida.

No abstract available now.

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Riener, C. R., Willingham D.B. (2001) Object identity and beliefs about object properties, Current Psychology of Cognition. 20(3-4), 255-260.

Comments on the article by F. Bedford which discussed a general law of numerical/object identity. The authors discuss beliefs about object identity and beliefs about object properties in perception.

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Proffitt, D. R., Creem, S. H. & Zosh, W. (2001). Seeing mountains in mole hills: Geographical slant perception. Psychological Science, 12, 418-423.

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 2) 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.

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Creem,S. H., Wraga, M., & Proffitt, D.R. (2001). Imagining physically impossible self-rotations: Geometry is more important than gravity. Cognition, 81,41-64.

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 array, requiring a rotation in the observer's 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 observer's principal axis.

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Creem, S. H., & Proffitt, D. R. (2001). Grasping objects by their handles: A necessary interaction between cognition and action. Journal of Experimental Psychology: Human Perception and Performance, 27, 218-228.

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 suggest 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.

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Creem, S. H., Downs, T. H., Wraga, M., Harrington, G. S., Proffitt, D. R. & Downs, III, J. H. ( 2001). An fMRI study of imagined self-rotation. Journal of Cognitive, Affective, & Behavioral Neuroscience, 1, 239-249.

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 task 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.

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Creem, S. H. & Proffitt, D. R. (2001). Defining the cortical visual systems: "What", "where", and "how". Acta Psychologica, 107, 43-68.

The visual system historically has been defined as consisting of at least two broad subsystems subserving object and spatial vision. These visual processing streams have been organized both structurally as two distinct pathways in the brain, and functionally for the types of tasks that they mediate. The classic definition by Ungerleider and Mishkin labeled a ventral "what" stream to process object information and a dorsal "where" stream to process spatial information. More recently, Goodale and Milner redefined the two visual systems with a focus on the different ways in which visual information is transformed for different goals. They relabeled the dorsal sream as a "how" system for transforming visual information using an egocentric frame of reference in preparation for direct action. This paper reviews recent research from psychophysics, neurophysiology, neuropsychology, and neuroimaging to define the roles of the ventral and dorsal visual processing streams. We discuss a possible solution that allows for both "where" and "how" systems that are functionally and structurally organized within the posterior parietal lobes.

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Carpenter, M. & Proffitt, D. R. (2001). Comparing viewer and array mental rotations in different planes. Memory & Cognition, 29, 441-448.

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.

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Wraga, M., Creem, S. H., & Proffitt, D. R. (2000). Perception-action dissociations of a walkable Muller-Lyer configuration. Psychological Science, 11, 239-243.

These studies examined the role of spatial encoding in inducing perception-action dissociations in visual illusions. Participants were shown a large-scale Muller-Lyer configuration with hoops as its tails. In Experiment 1, participants either made verbal estimates of the extent of the Muller-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.

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Wraga, M., Creem, S. H., & Proffitt, D. R. (2000). Updating displays after imagined object- and viewer rotations. Journal of Experimental Psychology: Learning, Memory, and Cognition. 26(1), 151-168.

Six experiments assessed the relative advantage of spatial updating during imagined viewer- and object-rotations. In the first two, participants updated the locations of four objects in an array after making imagined rotations of themselves around the array (Viewer), or of the array itself (Array). Participants responded faster and made fewer errors in Viewer than in Array, while positioned outside (Experiment 1) or inside (Experiment 2) the array. In Experiment 3, an apparent Array advantage for updating objects rather than locations was attributable to the fact that participants had performed imagined translations of single objects rather than rotations of the entire array. Using the location updating task, superior performance in Viewer persisted even when the four-object array was collapsed into a single object (Experiment 4); however, rotations of an object with a highly familiar configuration (Experiment 5) improved Object rotation performance somewhat. A final experiment found near-Viewer levels of Object performance when the imagined rotation was accompanied by haptic information for the turning object. We attributed these findings to the relative differences in the way the spatial reference frames corresponding to each imagined rotation are transformed by the human cognitive system.

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Wraga, M. & Proffitt, D.R. (2000). Mapping the zone of eye height utility for seated and standing observers. Perception, 29, 1361-1383.

In a series of experiments, we delimited a region within the veridical axis of space in which eye height (EH) information is used maximally to scale object heights, referred to as the "zone of eye height utility" (Wraga, 1999b Journal of Experimental Psychology, Human Perception and Performance 25 518-530). To test the lower limit of the zone, linear perspective (on the floor) was varied via introduction of a false perspective (FP) gradient while all sources of EH information except linear perspective were held constant. For seated (experiment 1a) observers, the FP gradient produced overestimations of height for rectangular objects up to 0.15 EH tall. This value was taken to be just outside the lower limit of the zone. This finding was replicated in a virtual environment, for both seated (experiment 1b) and standing (experiment 2) observers. For the upper limit of the zone, EH information itself was manipulated by lowering observers' center of projection in a virtual scene. Lowering the effective EH of standing (experiment 3) and seated (experiment 4) observers produced corresponding overestimation of height for objects up to about 2.5 EH. This zone of approximately 0.20-0.25 EH suggests that the human visual system weights size information differentially, depending on its efficacy.

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Dixon, M. W, Wraga, M, Proffitt, D. R., Williams, G. C. (2000). Eye height scaling of absolute size in immersive and nonimmersive displays. Journal of Experimental Psychology: Human Perception & Performance. 26(2), 582-593.

Eye-height (EH) scaling of absolute height was investigated in three experiments. In Experiment 1, standing observers viewed cubes in an immersive virtual environment. Observers' center of projection was placed at actual EH and at 0.7 times actual EH. Observers' size judgments revealed that the EH manipulation was 76.8% effective. In Experiment 2, seated observers viewed the same cubes on an interactive desktop display; however, no effect of EH was found in response to the simulated EH manipulation. Experiment 3 tested standing observers in the immersive environment with the field of view reduced to match that of the desktop. Comparable to Experiment 1, the effect of EH was 77%. These results suggest that EH scaling is not generally used when people view an interactive desktop display because the altitude of the center of projection is indeterminate. EH scaling is spontaneously evoked, however, in immersive environments.

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Bhalla, M., & Proffitt, D.R. (2000). Geographical slant perception: Dissociation and coordination between explicit awareness and visually guided actions. In Y. Rossetti and A. Revonsuo (Eds.), Dissociation but Interaction between Nonconscious and Conscious Processing. Amsterdam: John Benjamins.

In four experiments, it was shown that hills appear steeper to people who are encumbered by wearing a heavy backpack (Experiment 1), are fatigued (Experiment 2), are of low physical fitness (Experiment 3), or are elderly and/or in declining health (Experiment 4). Visually guided actions are unaffected by these manipulations of physiological potential. Although dissociable, the awareness and action systems were also shown to be interconnected. Recalibration of the transformation relating awareness and actions was found to occur only over long-term changes in physiological potential (fitness level, age and health) but not with transitory changes (fatigue and load). Findings are discussed in terms of a time-dependent coordination between the separate systems that control explicit visual awareness and visually guided action.

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Bertamini, M, & Proffitt, D R. (2000). Hierarchical motion organization in random dot configurations. Journal of Experimental Psychology: Human Perception & Performance. 26(4), 1371-1386.

Motion organization has 2 aspects: the extraction of a (moving) frame of reference and the hierarchical organization of moving elements within the reference frame. Using a discrimination of relative motions task, the authors found large differences between different types of motion (translation, divergence, and rotation) in the degree to which each can serve as a moving frame of reference. Translation and divergence are superior to rotation. There are, however, situations in which rotation can serve as a reference frame. This is due to the presence of a second factor, structural invariants (SIs). SIs are spatial relationships persisting among the elements within a configuration such as a collinearity among points or one point coinciding with the center of rotation for another (invariant radius). The combined effect of these 2 factors--motion type and SIs--influences perceptual motion organization.

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Yang, T. L., Dixon, M. W., & Proffitt, D. R. (1999). Seeing big things: Overestimation of heights is greater for real objects than for objects in pictures. Perception. 28, 445-467.

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 that 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.

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Wraga, M., Creem, S. H., & Proffitt, D. R. (1999). The influence of spatial reference frames on imagined object- and viewer rotations. Acta Psychologica, 102, 247-264.

The human visual system can represent an object's spatial structure with respect to multiple frames of reference. It can 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 difficult than imagined viewer rotations. We reviewed several related research domains to understand this discrepancy in terms of the different reference frames associated with each imagined movement. An examination of the mental rotation literature revealed that observers' difficulties in predicting an object's rotational outcome may stem from a general deficit with imagining the cohesive rotation of the object's 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 viewer's relative frame are performed cohesively and are thus mostly immune to effects of other frames.

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Proffitt, D., & Banton, T. (1999). Perceived depth is enhanced with parallax scanning.: Technical report for Vision III Imaging.

No abstract available now.

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Proffitt, D. R. (1999). Naive physics. In R. Wilson & F. Keil (Eds.), The MIT encyclopedia of the cognitive sciences. Cambridge, MA: MIT Press.

No abstract available now.

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Proffitt, D. R. (1999). Perception: Ecological versus Inferential Approaches. In R. J. Sternberg (Ed.). The concept of cognition. Cambridge: MIT Press.

No abstract available now.

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Kaiser, M. K., Proffitt, D. R., Banton, T., & Steve, J. (1999). Learning to walk on other worlds: Simulation of alternative gravitational / inertial environments.

No abstract available now.

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Creem, S. H., & Proffitt, D. R. (1999). Separate memories for visual guidance and explicit awareness: The roles of time and place. Challis, Bradford H. (Ed), Velichkovsky, Boris M. (Ed), et al. (1999). Stratification in cognition and consciousness. Advances in consciousness research. (pp. 73-104). Amsterdam, Netherlands: John Benjamins Publishing Company. viii, 293 pp.

Illustrates the roles of time and place in memory for visual guidance and explicit awareness. The topics discussed include stratification in perception and memory (perceptual awareness and visual guidance, frames of reference, a role for time and place) and memory for action and awareness (2 memories for geographical slant, memorial judgments given in the presence of the hill, memorial judgments given away from the hill, geographical slant conclusions). The work involving judgments of geographical slant shows that visual guidance memory for hills lasts for at least 2 mins, longer than found in research on pointing or saccades. For judgments of the incline of hills, the response is tied to the location in which the hill was perceived. The author's findings suggests that memories for visual guidance and explicit awareness are dissociated in the short term within the presence of the stimulus. However, with the addition of longer time delays, or by removing the observer from the surroundings, communication between conscious awareness and visual guidance is necessary. Visual guidance memory is not preserved in these cases, and the authors found that actions are thus informed by the explicit visual representation stored in memory.

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Bhalla, M., & Proffitt, D. R. (1999). Visual-Motor recalibration in geographical slant perception. Journal of Experimental Psychology: Human Perception & Performance. 25(4), 1076-1096.

In 4 experiments, it was shown that hills appear steeper to people who are encumbered by wearing a heavy backpack (Experiment 1), are fatigued (Experiment 2), are of low physical fitness (Experiment 3), or are elderly and/or in declining health (Experiment 4). Visually guided actions are unaffected by these manipulations of physiological potential. Although dissociable, the awareness and action systems were also shown to be interconnected. Recalibration of the transformation relating awareness and actions was found to occur over long-term changes in physiological potential (fitness level, age, and health) but not with transitory changes (fatigue and load). Findings are discussed in terms of a time-dependent coordination between the separate systems that control explicit visual awareness and visually guided action.

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Creem, S.H., & Proffitt, D.R. (1998). Two memories for geographical slant: Separation and interdependence of action and awareness. Psychonomic Bulletin & Review, 5, 22-36.

Extends 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, Ss' 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, Ss' motoric responses increased along with the increase in verbal reports. These results suggest 2 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.

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Proffitt, D. R., Bhalla, M., Gossweiler, R., & Midgett, J. (1995). Perceiving geographical slant. Psychonomic Bulletin & Review, 2(4), 409-428.

Conducted 5 experiments with 610 undergraduates to examine Ss' judgment of the inclination of hills viewed either out-of-doors or in a computer-simulated virtual environment. Angle judgments were obtained by having Ss (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 1st 2 measures, but not the 3rd. It is proposed that the perceived exaggeration of geographical slant preserves the relationship between distal inclination and people's behavioral potential. Apparent slant increased with fatigue. Visually guided actions were 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. (PsycINFO Database Record (c) 2005 APA, all rights reserved)

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Hecht, H., & Proffitt, D. R. (1995). The price of expertise : Effects of experience on the Water-Level Task. Psychological Science, 6(2), 90-95.

When shown a tilted container, people often fail to appreciate that the surface of the liquid contained within should remain horizontal with respect to the ground. This study investigated how amenable this bias is to experience in relevant everyday situations. Surprisingly, liquid surfaces that waitresses and bartenders considered natural deviated even more from horizontal than was the case for comparison groups. This finding is, to our knowledge, the only documented case in which performance declines with experience. We suggest that practical experience promotes a functionally relative perspective, in which the orientation of the liquid's surface is evaluated relative to that of its container as opposed to being related directly to the surrounding environment. The container-relative perspective, in turn, evokes a perceptual bias that is responsible for the systematic errors observed on this task.

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Gossweiler, R., Proffitt, D.R., Bhalla, M., & Pausch, R. (1995). A hill study: Using a virtual environment as a perceptual psychology laboratory. IEEE Computer: Special Issue on Real Applications for Virtual Reality, March

No abstract available now.

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