Egocentric Distance Perception Research Articles

Evidence for the embodiment of space perception: concurrent hand but not arm action moderates reachability and egocentric distance perception

The perception of reachability (i.e., whether an object is within reach) relies on body representations and action simulation. Similarly, egocentric distance estimation (i.e., the perception of the distance an object is from the self) is thought to be partly derived from embodied action simulation. Although motor simulation is important for both, it is unclear whether the cognitive processes underlying these behaviors rely on the same motor processes. To investigate this, we measured the impact of a motor interference dual-task paradigm on reachability judgment and egocentric distance estimation, while allocentric length estimation (i.e., how distant two stimuli are from each other independent from the self) was used as a control task. Participants were required to make concurrent actions with either hand actions of foam ball grip squeezing or arm actions of weight lifting, or no concurrent actions. Results showed that concurrent squeeze actions significantly slowed response speed in the reachability judgment and egocentric distance estimation tasks, but that there was no impact of the concurrent actions on allocentric length estimation. Together, these results suggest that reachability and distance perception, both egocentric perspective tasks, and in contrast to the allocentric perspective task, involve action simulation cognitive processes. The results are discussed in terms of the implication of action simulation when evaluating the position of a target relative to the observer’s body, supporting an embodied view of spatial cognition.

Exploratory movement generates higher-order information that is sufficient for accurate perception of scaled egocentric distance.

Body movement influences the structure of multiple forms of ambient energy, including optics and gravito-inertial force. Some researchers have argued that egocentric distance is derived from inferential integration of visual and non-visual stimulation. We suggest that accurate information about egocentric distance exists in perceptual stimulation as higher-order patterns that extend across optics and inertia. We formalize a pattern that specifies the egocentric distance of a stationary object across higher-order relations between optics and inertia. This higher-order parameter is created by self-generated movement of the perceiver in inertial space relative to the illuminated environment. For this reason, we placed minimal restrictions on the exploratory movements of our participants. We asked whether humans can detect and use the information available in this higher-order pattern. Participants judged whether a virtual object was within reach. We manipulated relations between body movement and the ambient structure of optics and inertia. Judgments were precise and accurate when the higher-order optical-inertial parameter was available. When only optic flow was available, judgments were poor. Our results reveal that participants perceived egocentric distance from the higher-order, optical-inertial consequences of their own exploratory activity. Analysis of participants’ movement trajectories revealed that self-selected movements were complex, and tended to optimize availability of the optical-inertial pattern that specifies egocentric distance. We argue that accurate information about egocentric distance exists in higher-order patterns of ambient energy, that self-generated movement can generate these higher-order patterns, and that these patterns can be detected and used to support perception of egocentric distance that is precise and accurate.

Eye Height Manipulations

Virtual reality technology can be considered a multipurpose tool for diverse applications in various domains, for example, training, prototyping, design, entertainment, and research investigating human perception. However, for many of these applications, it is necessary that the designed and computer-generated virtual environments are perceived as a replica of the real world. Many research studies have shown that this is not necessarily the case. Specifically, egocentric distances are underestimated compared to real-world estimates regardless of whether the virtual environment is displayed in a head-mounted display or on an immersive large-screen display. While the main reason for this observed distance underestimation is still unknown, we investigate a potential approach to reduce or even eliminate this distance underestimation. Building up on the angle of declination below the horizon relationship for perceiving egocentric distances, we describe how eye height manipulations in virtual reality should affect perceived distances. In addition, we describe how this relationship could be exploited to reduce distance underestimation for individual users. In a first experiment, we investigate the influence of a manipulated eye height on an action-based measure of egocentric distance perception. We found that eye height manipulations have similar predictable effects on an action-based measure of egocentric distance as we previously observed for a cognitive measure. This might make this approach more useful than other proposed solutions across different scenarios in various domains, for example, for collaborative tasks. In three additional experiments, we investigate the influence of an individualized manipulation of eye height to reduce distance underestimation in a sparse-cue and a rich-cue environment. In these experiments, we demonstrate that a simple eye height manipulation can be used to selectively alter perceived distances on an individual basis, which could be helpful to enable every user to have an experience close to what was intended by the content designer.

Effect of total sleep deprivation on egocentric distance estimation following a fatiguing task

The aim of this study was to investigate the effect of a total sleep deprivation (TSD) on the egocentric distance estimation following a fatiguing task (i.e. sprint repetitions). Ten soccer players (age: 22.8 ± 1.3 years; weight: 72. 8 ± 10 .5 kg; height: 1.8 ± 0.03 m) were volunteered to participate in the study. Subjects were invited to estimate different distances in two different sessions (i) following a reference night and (ii) following a night of TSD. The distance estimation consists to perceive three different distances (15, 25, and 35 m) before and after a repeated sprint exercise on a cycloergometer. The results demonstrated a significant effect of TSD on the perception of egocentric distance (F (1.9) = 11.22, p < 0.01). Indeed, the results showed an underestimation (compression of the real distance) of all distances at rest and following the repeated sprint exercise. Additionally, the underestimation was more acute after the fatiguing task. TSD affects the estimation of egocentric distance by soccer players at rest and following fatiguing task.

Angular declination and the dynamic perception of egocentric distance.

The extraction of the distance between an object and an observer is fast when angular declination is informative, as it is with targets placed on the ground. To what extent does angular declination drive performance when viewing time is limited? Participants judged target distances in a real-world environment with viewing durations ranging from 36-220 ms. An important role for angular declination was supported by experiments showing that the cue provides information about egocentric distance even on the very first glimpse, and that it supports a sensitive response to distance in the absence of other useful cues. Performance was better at 220-ms viewing durations than for briefer glimpses, suggesting that the perception of distance is dynamic even within the time frame of a typical eye fixation. Critically, performance in limited viewing trials was better when preceded by a 15-s preview of the room without a designated target. The results indicate that the perception of distance is powerfully shaped by memory from prior visual experience with the scene. A theoretical framework for the dynamic perception of distance is presented.

Gaze behavior and the perception of egocentric distance.

The ground plane is thought to be an important reference for localizing objects, particularly when angular declination is informative, as it is for objects seen resting at floor level. A potential role for eye movements has been implicated by the idea that information about the nearby ground is required to localize objects more distant, and by the fact that the time course for the extraction of distance extends beyond the duration of a typical eye fixation. To test this potential role, eye movements were monitored when participants previewed targets. Distance estimates were provided by walking without vision to the remembered target location (blind walking) or by verbal report. We found that a strategy of holding the gaze steady on the object was as frequent as one where the region between the observer and object was fixated. There was no performance advantage associated with making eye movements in an observational study (Experiment 1) or when an eye-movement strategy was manipulated experimentally (Experiment 2). Observers were extracting useful information covertly, however. In Experiments 3 through 5, obscuring the nearby ground plane had a modest impact on performance; obscuring the walls and ceiling was more detrimental. The results suggest that these alternate surfaces provide useful information when judging the distance to objects within indoor environments. Critically, they constrain the role for the nearby ground plane in theories of egocentric distance perception.

Three theories for reconciling the linearity of egocentric distance perception with distortion of shape on the ground plane.

The focus here is on the paradoxical finding that whereas visually perceived egocentric distance is proportional to physical distance out to at least 20 m under full-cue viewing, there are large distortions of shape within the same range, reflecting a large anisotropy of depth and frontal extents on the ground plane. Three theories of visual space perception are presented, theories that are relevant to understanding this paradoxical result. The theory by Foley, Ribeiro-Filho, and Da Silva is based on the idea that when the visual system computes the length of a visible extent, the effective visual angle is a non-linear increasing function of the actual visual angle. The theory of Durgin and Li is based on the idea that two angular measures, optical slant and angular declination, are over-perceived. The theory of Ooi and He is based on both a default perceptual representation of the ground surface in the absence of visual cues and the “sequential surface integration process” whereby an internal representation of the visible ground surface is constructed starting from beneath the observer’s feet and extending outward. Keywords: visual space perception, vision, depth perception.

The perception of egocentric distances in virtual environments - A review

Over the last 20 years research has been done on the question of how egocentric distances, i.e., the subjectively reported distance from a human observer to an object, are perceived in virtual environments. This review surveys the existing literature on empirical user studies on this topic. In summary, there is a mean estimation of egocentric distances in virtual environments of about 74% of the modeled distances. Many factors possibly influencing distance estimates were reported in the literature. We arranged these factors into four groups, namely measurement methods, technical factors, compositional factors, and human factors. The research on these factors is summarized, conclusions are drawn, and promising areas for future research are outlined.

Egocentric distance perception in large screen immersive displays

Many scientists have demonstrated that compared to the real world egocentric distances in head-mounted display virtual environments are underestimated. However, distance perception in large screen immersive displays has received less attention. We investigate egocentric distance perception in a virtual office room projected using a semi-spherical, a Max Planck Institute CyberMotion Simulator cabin and a flat large screen immersive display. The goal of our research is to systematically investigate distance perception in large screen immersive displays with commonly used technical specifications. We specifically investigate the role of distance to the target, stereoscopic projection and motion parallax on distance perception. We use verbal reports and blind walking as response measures for the real world experiment. Due to the limited space in the three large screen immersive displays we use only verbal reports as the response measure for the experiments in the virtual environment. Our results show an overall underestimation of distance perception in the large screen immersive displays, while verbal estimates of distances are nearly veridical in the real world. We find that even when providing motion parallax and stereoscopic depth cues to the observer in the flat large screen immersive display, participants estimate the distances to be smaller than intended. Although stereo cues in the flat large screen immersive display do increase distance estimates for the nearest distance, the impact of the stereoscopic depth cues is not enough to result in veridical distance perception. Further, we demonstrate that the distance to the target significantly influences the percent error of verbal estimates in both the real and virtual world. The impact of the distance to the target on the distance judgments is the same in the real world and in two of the used large screen displays, namely, the MPI CyberMotion Simulator cabin and the flat displays. However, in the semi-spherical display we observe a significantly different influence of distance to the target on verbal estimates of egocentric distances. Finally, we discuss potential reasons for our results. Based on the findings from our research we give general suggestions that could serve as methods for improving the LSIDs in terms of the accuracy of depth perception and suggest methods to compensate for the underestimation of verbal distance estimates in large screen immersive displays.

Visual Discomfort and Depth-of-Field

Visual discomfort has been reported for certain visual stimuli and under particular viewing conditions, such as stereoscopic viewing. In stereoscopic viewing, visual discomfort can be caused by a conflict between accommodation and convergence cues that may specify different distances in depth. Earlier research has shown that depth-of-field, which is the distance range in depth in the scene that is perceived to be sharp, influences both the perception of egocentric distance to the focal plane, and the distance range in depth between objects in the scene. Because depth-of-field may also be in conflict with convergence and the accommodative state of the eyes, we raised the question of whether depth-of-field affects discomfort when viewing stereoscopic photographs. The first experiment assessed whether discomfort increases when depth-of-field is in conflict with coherent accommodation–convergence cues to distance in depth. The second experiment assessed whether depth-of-field influences discomfort from a pre-existing accommodation–convergence conflict. Results showed no effect of depth-of-field on visual discomfort. These results suggest therefore that depth-of-field can be used as a cue to depth without inducing discomfort in the viewer, even when cue conflicts are large.

Audio, visual, and audio-visual egocentric distance perception by moving subjects in virtual environments

We present a study on audio , visual , and audio-visual egocentric distance perception by moving subjects in virtual environments. Audio-visual rendering is provided using tracked passive visual stereoscopy and acoustic wave field synthesis (WFS). Distances are estimated using indirect blind-walking (triangulation) under each rendering condition. Experimental results show that distances perceived in the virtual environment are systematically overestimated for rendered distances closer than the position of the audio-visual rendering system and underestimated for farther distances. Interestingly, subjects perceived each virtual object at a modality-independent distance when using the audio modality, the visual modality, or the combination of both. WFS was able to synthesise perceptually meaningful sound fields. Dynamic audio-visual cues were used by subjects when estimating the distances in the virtual world. Moving may have provided subjects with a better visual distance perception of close distances than if they were static. No correlation between the feeling of presence and the visual distance underestimation has been found. To explain the observed perceptual distance compression, it is proposed that, due to conflicting distance cues, the audio-visual rendering system physically anchors the virtual world to the real world. Virtual objects are thus attracted by the physical audio-visual rendering system.

Depth of Field Affects Perceived Depth-width Ratios in Photographs of Natural Scenes

The aim of the study was to find out how much influence depth of field has on the perceived ratio of depth and width in photographs of natural scenes. Depth of field is roughly defined as the distance range that is perceived as sharp in the photograph. Four different semi-natural scenes consisting of a central and two flanking figurines were used. For each scene, five series of photos were made, in which the distance in depth between the central figurine and the flanking figurines increased. These series of photographs had different amounts of depth of field. In the first experiment participants adjusted the position of the two flanking figurines relative to a central figurine, until the perceived distance in the depth dimension equaled the perceived lateral distance between the two flanking figurines. Viewing condition was either monocular or binocular (non-stereo). In the second experiment, the participants did the same task but this time we varied the viewing distance. We found that the participants' depth/width settings increased with increasing depth of field. As depth of field increased, the perceived depth in the scene was reduced relative to the perceived width. Perceived depth was reduced relative to perceived width under binocular viewing conditions compared to monocular viewing conditions. There was a greater reduction when the viewing distance was increased. As photographs of natural scenes contain many highly redundant or conflicting depth cues, we conclude therefore that local image blur is an important cue to depth. Moreover, local image blur is not only taken into account in the perception of egocentric distances, but also affects the perception of depth within the scene relative to lateral distances within the scene.

Influence of action execution on reachability and distance perception.

In the current literature, it is thought that the behaviours of reachability and distance perception rely on parietal lobe and motor system processes. For example, Coello et al. (2008; see also Coello & Delevoye-Turrell 2007) demonstrated that disruption of primary hand motor cortex moderated the decision of whether an object was reachable of not. This suggests that the perception of reachability or reach space appeared to rely on body representations and action simulation cognition. Similarly, other studies have demonstrated that distance perception can be moderated by the manipulated state of the body; for example by wearing a backpack (Proffitt, 2006), by having sport expertise (Witt, 2011) or by having the use of a tool (Witt, Proffitt & Epstein, 2005; Witt & Proffitt, 2008). These results suggest that the perception of space is derived from an embodied representation, as the environment seems to be perceived through the ability to act in it. Although we suggest here that reachability and distance perception might rely on similar cognitive representations, it remains unclear what differences exist between the two different behaviours, and moreover, whether there is a single common cognitive process underlying the behaviours. To investigate this, we measured spatial perception using reachability judgement and distance magnitude estimation tasks. The reachability judgement task measured participant’s judgements of whether a stimulus was within reach or not, and two distance magnitude estimation tasks measured the estimated distance between the participant and a stimulus (egocentric distance) or between two stimuli (allocentric distance). For the reachability judgement and egocentric distance magnitude estimation tasks, the same stimuli positions were used to allow for a direct comparison between the tasks. A further manipulation involved the participants making concurrent actions during the three tasks. These included hand actions of soft-ball grip squeezing, arm actions of weight lifting or the baseline comparison of no movements. We predicted that if action processes are needed for both the reachability and distance magnitude tasks, then performing an action at the same time might moderate the participant’s responses, measured by the reaction time and accuracy of response. Moreover, the aim was to investigate the differential impact of the motor disruption in allocentric and egocentric distance perception. Results showed that the motor disruption conditions had a significant impact on participant’s reaction time, with the grasping movements slowing the participant responses in the reachability judgement task and in the egocentric distance estimation task. However, the motor disruption conditions had no impact in the allocentric distance estimation task. None of the tasks showed any significant effects of motor disruption on accuracy. These findings confirm the existing literature as they show that executing concomitant actions moderated the perceptual tasks, suggesting that motor processes were necessary for the space cognition processes. Moreover, our data suggest that evaluating the distance separating two stimuli do not require action processes. The data are discussed in terms of how spatial cognition involves motor cognition that is body dependent.

Two distinct angular perceptual variables account for the dissociation between egocentric and exocentric distance perception

Two distinct angular perceptual variables account for the dissociation between egocentric and exocentric distance perception

Retinal blur and the perception of egocentric distance

A central function of vision is determining the layout and size of objects in the visual field, both of which require knowledge of egocentric distance (the distance of an object from the observer). A wide range of visual cues can reliably signal relative depth relations among objects, but retinal signals directly specifying distance to an object are limited. A potential source of distance information is the pattern of blurring on the retina, since nearer fixation generally produces larger gradients of blur on the extra-foveal retina. While prior studies implicated blur as only a qualitative cue for relative depth ordering, we find that retinal blur gradients can act as a quantitative cue to distance. Surfaces depicted with blur gradients were judged as significantly closer than those without, with the size of the effect modulated by the degree of blur, as well as the availability of other extra-retinal cues to distance. Blur gradients produced substantial changes in perceived distance regardless of relative depth relations of the surfaces indicated by other cues, suggesting that it operates as a robust cue to distance, consistent with the empirical relationship between blur and fixation distance.

Exploring the time course of egocentric distance perception with visual masking of a real-world environment

The mask effect was more compelling in the reduced cue context. Participants showed no distance sensitivity in the 50 ms masked condition and performance continued to improve with extended (1000 ms) viewing. Performance at the shortest viewing duration was better in the context of 1000-ms trials, suggesting the extraction of information benefi ted from experience acquired during the extended-viewing trials.

Does energy expenditure affect the perception of egocentric distance? A failure to replicate Experiment 1 of Proffitt, Stefanucci, and Epstein (2003)

Does energy expenditure affect the perception of egocentric distance? A failure to replicate Experiment 1 of Proffitt, Stefanucci, and Epstein (2003)

The effects of restricted viewing conditions on egocentric distance judgments

Egocentric distance perception under full-cue conditions has been shown to be accurate as revealed though visually directed action tasks. The present studies assessed the necessity of 1) binocular disparity, 2) full field of view and 3) seeing one's body standing on the ground plane, for accurate scaling of egocentric space at distances from 5 to 15 meters. An investigation of these viewing conditions is especially relevant to space perception in virtual environments in which restrictions are often present, and distance compression has been found. We provided complete pictorial depth cues (e.g., linear perspective, height in the plane, horizon ratio, familiar size) but restricted viewing conditions in a real-world egocentric distance judgment task. Participants walked to previously viewed targets on the ground plane at distances ranging from 5 to 15 meters using both direct and indirect walking tasks. The first study varied whether participants were able to view the supporting surface on which they were standing. Observers wore an occluding collar designed to block the view of their lower body and feet while viewing the target. A second study examined the influence of stereo over monocular viewing. A final study utilized three conditions varying field of view and restricting observers' ability to rotate their head. Vision was not restricted in the first condition. In the second condition, observers wore goggles to restrict field of view and could rotate their heads while viewing the target. In the third condition, observers wore the same goggles along with a cervical collar which constrained both head motion and the view of their feet on the ground. In all studies and all conditions, visually directed walking remained near veridical. These results emphasize the lack of influence of viewing restrictions on accurate egocentric distance judgments within 5 to 15 meters in the real-world and leave open the question of the factors influencing distance judgments in virtual environments.

Adaptation of egocentric distance perception under telestereoscopic viewing within reaching space

Telestereoscopic viewing provides a method to distort egocentric distance perception by artificially increasing the interpupillary distance. Adaptation to such a visual rearrangement is little understood. Two experiments were performed in order to dissociate the effects of a sustained increased vergence demand, from those of an active calibration of the vergence/distance mapping. Egocentric distances were assessed within reaching space through open-loop pointing to small targets in the dark. During the exposure condition of the first experiment, subjects were instructed to point to the targets without feedback, whereas in the second experiment, hand visual feedback was available, resulting in a modified relationship between vergence-specified distance and reach distance. The visual component of adaptation in the second experiment was assessed on the unexposed hand. In the post-tests of both experiments, subjects exhibited a constant distance overestimation across all targets, with a more than twice larger aftereffect in the second one. These findings suggest two different processes: (1) an alteration in the vergence effort following sustained increased vergence; (2) a calibration of the vergence/distance mapping uncovering the visual component of adaptation.

Does Energy Expenditure Affect the Perception of Egocentric Distance? A Failure to Replicate Experiment 1 of Proffitt, Stefanucci, Banton, and Epstein (2003)

In a series of recent studies, Proffitt and his colleagues have reported that the perceived distance to a target is influenced by the energy expenditure associated with any action, such as walking or throwing, for spanning the distance to the target. In particular, Proffitt, Stefanucci, Banton, and Epstein (2003) reported that wearing a heavy backpack caused verbal reports of distance to increase. We conducted a study to determine whether three responses dependent on perceived distance (verbal report of distance, blind walking, and estimates of object size) are influenced by the backpack manipulation. In two experiments, one involving a between-participants design and the other involving a within-participants design, we found that none of the three responses were influenced by the wearing of a heavy backpack.