Publications

Forthcoming

Proffitt, D. R., Linkenauger, S. A., P. Y. Lin, L., & Taylor, R. L. (Forthcoming).

Body scaling of visually perceived metric space

. In . M. Longo & A. Alsmith (Eds.) Handbook of Bodily Awareness, London, UK: Routledge.

Eyes evolved to detect the directions from which ambient luminance contrasts emanate. With
varying degrees of acuity, both compound and simple chambered eyes register the angular
position of visual features relative to either the fovea (azimuth and elevation) or to other visual
features in the scene. Optic flow (dynamical changes in this angular information) is sufficient to
specify unit-less aspects of the spatial visual world such as 3-dimensional form (à la the kinetic
depth effect) or depth order (via dynamic occlusion). However, other aspects of the visual
world, such as perceived size and extent, require a combining of visual angles with appropriate
metrics, and in many cases, the body provides these requisite perceptual rulers. For example, via
a simple trigonometric formula, the angular elevation of visual features viewed on the ground
plane specifies their distance from the observer in units of eye-height.
The body provides a plethora of perceptual rules, each specific to the ongoing activity of the
perceiver. For example, the sizes of graspable objects are perceived relative to the size of one’s
hand, whereas the distance across an open field is scaled by how much walking will be required
to traverse it. The literature on perceptual body scaling is divided into three general classes.
Morphological scaling uses the metrics of the body’s skeletal structure—eye height, arm’s
length, hand size—and its extension through the wielding of tools. Physiological scaling draws
on the body’s internal, often metabolic, states as they relate to intended actions. For example,
the amount of walking required to traverse an extent is scaled by the bioenergetic costs of
locomotion. Finally, behavioral scaling is provided by the efficacy of intended actions.
Research on embodied perception addresses the following question: By what units are metric
spatial perceptions scaled? As summarized in this chapter, the solution to this problem is a
specification of what aspects of the body are used to scale spatial percepts given the observer’s
phenotype and the intended actions afforded by their physical surroundings. Roughly 100
research articles are reviewed.

Clore, G. L., Proffitt, D. R., & Zadra, J. R. (Forthcoming). Feeling, seeing, and liking: How bodily resources inform perception and emotion. In M. D. Robinson & L. E. Thomas (Eds.) Embodied Psychology: Thinking, Feeling, and Acting . New York, NY: Springer.

Perception of the physical environment and emotions about the social environment are integrated into a resource-based account. Animals, unlike plants, must move around their environment to obtain resources and avoid predators, which in turn necessitates perception. Animate creatures also must coordinate perceptions of their internal and external environments to balance bodily expenditures of energy and environmental demands. Consequently, perceptions of distances and the steepness of hills increase with exhaustion and glucose depletion and decrease with physical fitness. They also increase with emotions of sadness and fear and decrease with accessibility to social resources. Social support when individuals are under stress even increases available glucose in the blood. The extraordinary success of the human species is believed to have depended on their living in cooperative social groups. Hence, social inclusion is a valuable resource. We propose an emotion-as-information model in which emotions serve as information for managing resources, especially social resources.  

2021

Weser, V. U., & Proffitt, D. R. (2021).

Expertise in tool use promotes tool embodiment

. Topics in Cognitive Science.

Body representations are known to be dynamically modulated or extended through tool use. Here, we review findings that demonstrate the importance of a user's tool experience or expertise for successful tool embodiment. Examining expert tool users, such as individuals who use tools in professional sports, people who use chopsticks at every meal, or spinal injury patients who use a wheelchair daily, offers new insights into the role of expertise in tool embodiment: Not only does tool embodiment differ between novices and experts, but experts may experience enhanced changes to their body representation when interacting with their own, personal tool. The findings reviewed herein reveal the importance of assessing tool skill in future studies of tool embodiment.

2020

2019

Linkenauger, S. A., Weser, V., & Proffitt, D. R. (2019). Choosing efficient actions: Deciding where to walk. PLoS ONE, 14, e0219729.
Humans evolved to be endurance animals. Our ancestors were persistence hunters; they would chase animals, including gazelles, until they ran them into exhaustion. Put simply, people evolved in an ecological niche that selected for endurance and efficiency of locomotion. To locomote to any destination, one could take countless different paths, each requiring different amounts of energy. Because the ground is typically not flat or homogeneous, the straight direct path is often not the most energetically efficient. For hills below 14°, the direct straight path up the hill is the most energetically efficient. However, for hills above 14°, walkers would minimize their absolute energy expenditure by taking a zigzagged path so that their gradient of ascension is 14° [1]. In three experiments, we assessed the degree to which people make bioenergetically efficient decisions about locomotion through path selection. In Experiment 1, people were immersed into a virtual environment and adjusted the angle of ascension of a virtual path up hills of various gradients so that when taking the path, they would expend the least amount of energy when they reached the top. The second experiment was of a similar design, but was conducted in the real word. In the last experiment, in a virtual environment, participants choose between two paths up hills of various gradient, where these paths varied in the energy required for ascent. Participants made these judgements both before and after motor experience with gradient climbing on an incline trainer. For steep hills, we found that people choose much straighter paths over the bioenergetically optimal zigzagged paths. Motor experience did lead to higher probability for choosing optimal paths for steep hills, but lead to less optimal paths for shallower ones. These results show clearly that individuals show a straight path bias when deciding how to ascend hills.
Twedt, E., Rainey, R. M., & Proffitt, D. R. (2019). Beyond nature: The roles of visual appeal and individual differences in perceived restorative potential. Journal of Environmental Psychology, 65, 1-11.
Natural environments are typically judged to be more restorative than built environments in terms of fostering recovery from stress or buffering against resource depletion. But this comparison tends to be categorical – nature versus built environments – and consequently, questions remain regarding the restorative potential of environments that do not fit into these categories. Furthermore, individual differences in evaluations of perceived restorative potential is not well understood. In Study 1, participants rated the perceived restorative potential of environments that ranged on a continuum from natural to built. Environmental attributes and individual differences were measured to predict perceived restorative potential. In Study 2, we measured the relationship between self-reported need-for-restoration and perceived restorative potential. The results support an account of perceived restorative potential that emphasizes the importance of visual appeal, naturalness, and an absence of people as important environment dimensions. These factors are influenced very little by assessed individual differences other than perceived need-for-restoration.
Weser, V. U., & Proffitt, D. (2019). Tool embodiment: The tool’s output must match the user’s input. Frontiers in Human Neuroscience, 11.
The embodiment of tools and rubber hands is believed to involve the modification of two separate body representations: the body schema and the body image, respectively. It is thought that tools extend the capabilities of the body’s action schema, whereas prosthetics like rubber hands are incorporated into the body image itself. Contrary to this dichotomy, recent research demonstrated that chopsticks can be embodied perceptually during a modified version of the rubber hand illusion (RHI) in which tools are held by the rubber hand and by the participant. In the present research, two experiments examined tool morpho-functional (tool output affordance, e.g., precision grasping) and sensorimotor (tool input, e.g., precision grip) match as a mechanism for this tool-use dependent change to the body image. Proprioceptive drift in the RHI occurred when the tool’s output and the user’s input matched, but not when this match was absent. This suggests that this factor may be necessary for tools to interact with the body image in the RHI.
We developed a novel interaction technique that allows virtual reality (VR) users to experience “weight” when hefting virtual, weightless objects. With this technique the perception of weight is evoked via constraints on the speed with which objects can be lifted. When hefted, heavier virtual objects move slower than lighter virtual objects. If lifters move faster than the lifted object, the object will fall. This constraint causes lifters to move slowly when lifting heavy objects. In two studies we showed that the size-weight illusion (SWI) is evoked when this technique is employed. The SWI occurs when two items of identical weight and different size are lifted and the smaller item is perceived as heavier than the larger item. The persistence of this illusion in VR indicates that participants bring their real-world knowledge of the relationship between size and weight to their virtual experience, and suggests that our interaction technique succeeds in making the visible tangible.

2018

Proffitt, D. (2018). Light and life: The evolution of visual perception. In . In J. Feldman & R. Stilling (Eds.), What Should I Read Next” 70 University of Virginia Professors Recommend Readings in History, Politics, Literature, Math, Science, Technology, the Arts, and More (pp. 85-89). University of Virginia Press.
Twedt, E., & Proffitt, D. (2018). Perception. In D. S. Dunn (Ed.), Oxford Bibliographies in Psychology. Oxford University Press.