Publications

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.
Weast, R. A., & Proffitt, D. (2018). Can I reach that? Blind reaching as an accurate measure of estimated reachable distance. Consciousness and Cognition, 64, 121–134.
Judgments of one’s reach extent have been repeatedly found to be overestimated by about 10%. In 3 studies, a new dependent measure was employed in which participants viewed targets, closed their eyes, and then touched the location of the remembered target or pointed to its location if out of reach. This experimental paradigm yielded a much smaller but still present bias to over-estimate by about 2%. In addition, participants often reached for and touched target locations that were actually out of reach in a manner indicative of the typical 10% over-estimation bias. Surprisingly, participant response accuracy improved significantly and consistently across experimental trials even without visual or tactile feedback. This suggests that the proprioceptive information about the arm in space coupled with the remembered visual information about target location were sufficient to facilitate learning.

2017

Gross, E. B., & Proffitt, D. (2017). The economy of social resources and its influence on spatial perceptions. In Perspective taking: Building a neurocognitive framework for integrating the “Social” and the “Spatial” (pp. 218-222). Frontiers Media SA.
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.
Weser, V., Finotti, G., Costantini, M., & Proffitt, D. (2017). Multisensory integration induces body ownership of a handtool, but not any handtool. Consciousness and Cognition, 56, 150–164.
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.

2016

Zadra, J., Weltman, A., & Proffitt, D. (2016). Walkable distances are bioenergetically scaled. Journal of Experimental Psychology: Human Perception and Performance, 42, 39-51.
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.
Clore, G., & Proffitt, D. (2016). The myth of pure perception. Behavioral and Brain Sciences, 39.
Firestone & Scholl (F&S) assume that pure perception is unaffected by cognition. This assumption is untenable for definitional, anatomical, and empirical reasons. They discount research showing nonoptical influences on visual perception, pointing out possible methodological “pitfalls.” Results generated in multiple labs are immune to these “pitfalls,” suggesting that perceptions of physical layout do indeed reflect bioenergetic resources.
Twedt, E., Rainey, R., & Proffitt, D. (2016). Designed natural spaces: informal gardens are perceived to be more restorative than formal gardens. Frontiers in Psychology, 7.
Experimental research shows that there are perceived and actual benefits to spending time in natural spaces compared to urban spaces, such as reduced cognitive fatigue, improved mood, and reduced stress. Whereas past research has focused primarily on distinguishing between distinct categories of spaces (i.e., nature vs. urban), less is known about variability in perceived restorative potential of environments within a particular category of outdoor spaces, such as gardens. Conceptually, gardens are often considered to be restorative spaces and to contain an abundance of natural elements, though there is great variability in how gardens are designed that might impact their restorative potential. One common practice for classifying gardens is along a spectrum ranging from “formal or geometric” to “informal or naturalistic,” which often corresponds to the degree to which built or natural elements are present, respectively. In the current study, we tested whether participants use design informality as a cue to predict perceived restorative potential of different gardens. Participants viewed a set of gardens and rated each on design informality, perceived restorative potential, naturalness, and visual appeal. Participants perceived informal gardens to have greater restorative potential than formal gardens. In addition, gardens that were more visually appealing and more natural-looking were perceived to have greater restorative potential than less visually appealing and less natural gardens. These perceptions and precedents are highly relevant for the design of gardens and other similar green spaces intended to provide relief from stress and to foster cognitive restoration.
Weser, V., Hesch, J., Lee, J., & Proffitt, D. (2016). User sensitivity to speed-and height-mismatch in VR. Proceedings of the ACM Symposium on Applied Perception, 143.

Facebook's purchase of Oculus VR in 2014 ushered in a new era of consumer virtual reality head-mounted displays (HMDs). Converging technological advancements in small, high-resolution displays and motion-detection devices propelled VR beyond the purview of high-tech research laboratories and into the mainstream. However, technological hurdles still remain. As more consumer grade products develop, user comfort and experience will be of the utmost importance. One of the biggest issues for HMDs that lack external tracking is drift in the user position and rotation sensors. Drift can cause motion sickness and make stationary items in the virtual environment to appear to shift in position. For developers who seek to design VR experiences that are rooted in real environments, drift can create large errors in positional tracking if left uncorrected over time. Although much of the current VR hardware makes use of external tracking devices to mitigate positional and rotational drift, the creation of head-mounted displays that can operate without the use of extremal tracking devices would make VR hardware more portable and flexible, and may therefore be a goal for future development.

Until technology advances sufficiently to completely overcome the hardware problems that cause drift, software solutions are a viable option to correct for it. It may be possible to speed up and slow down users as they move though the virtual world in order to bring their tracked position back into alignment with their position in the real world. If speed changes can be implemented without users noticing the alteration, it may offer a seamless solution that does not interfere with the VR experience.

In Experiments 1 and 2, we artificially introduced speed changes that made users move through the VR environment either faster than or slower than their actual real-world speed. Users were tasked with correctly identifying when they were moving at the correct true-to-life speed when compared to an altered virtual movement speed. Fore and aft movement and movement from side to side initiated by seated users bending at the waist were tested separately in two experiments. In Experiment 3, we presented alternating views of the virtual scene from different user heights. In this study, users had to correctly distinguish the view of the virtual scene presented at the correct height from incorrect shorter and taller heights.

In Experiments 1 and 2, we found that on average speed increases and decreases up to approximately 25% went unnoticed by users, suggesting that there is flexibility for programs to add speed changes imperceptible to users to correct for drift. In contrast, Experiment 3 demonstrates that on average users were aware of height changes after virtual heights were altered by just 5 cm. These thresholds can be used by VR developers to compensate for tracking mismatches between real and virtual positions of users of virtual environments, and also by engineers to benchmark new virtual reality hardware against human perceptual abilities.

Zadra, J., & Proffitt, D. (2016). Optic flow is calibrated to walking effort. Psychonomic Bulletin & Review, 23(5), 1491–1496.
Through experience, people learn that a given magnitude of walking produces an associated magnitude of optic flow. Artificially altering this relationship has both behavioral and perceptual consequences: walking on a treadmill results in zero translational optic flow and causes people to subsequently drift forward when attempting to walk in place while blindfolded (they have learned that forward walking is required to remain stationary). Similarly, after walking on a treadmill people perceive the walking distance to targets to be greater (they have recalibrated the magnitude of walking required to reach the target). While the measurement unit for walking magnitude in this relationship has been treated as walking speed (stride length * [steps / time]), recent experiments suggest that walkable distances may instead be measured in bioenergetic units (i.e., the magnitude of energy required to produce a given magnitude of optic flow). In the first experiment, zero translational optic flow was paired with a constant walking speed, and walking energy was manipulated by varying the incline of the treadmill. Participants who walked on an inclined treadmill drifted farther while attempting to walk in place than participants who walked on a flat treadmill. A follow-up experiment presented optic flow via an immersive virtual environment, and no difference between flat and inclined treadmill walking was found, thereby showing that the effect found in the first experiment was not an artifact of biomechanical differences associated with flat versus inclined treadmill walking. The results support the hypothesis that walking magnitude is scaled by bioenergetic units.