Binocular distance perception: egocentric distance tasks

This study extends and tests a theory of binocular distance perception that has been shown to give a good account of performance in relative distance tasks. Here the theory is tested in two experiments in which the observer directly indicates perceived egocentric distance of targets (perceived distance from himself or herself) by means of a verbal report or manual pointing response. In the first, the distance to two targets is varied while maintaining a constant disparity between them. In the second, one target is held fixed while the distance to a second target is varied. In each case, the observer indicates the perceived distance of each target. Manual and verbal responses are found to agree with each other to within a linear transform. Both sets of data are shown to be consistent with the theory and are used to estimate the parameters of the theory. There is no other theory that predicts these results.     

Perceived size and distance as a perceptual conflict between two processing modes

Three different sized squares were successively presented at the same physical distance under three observational conditions which provided different information about distance in the visual field. The 60 observers in each observational condition were asked to give verbal absolute judgments of perceived size and perceived distance for each of the squares. The results showed that in a full-cue situation a ratio of perceived absolute sizes is equal to that of the corresponding visual angles, with perceived distances appearing equal to each other; in a reduced-cue situation an object of smaller perceived size is judged to be farther away than one of larger perceived size, with the observers tending to assume the two objects as the same object or identically sized objects. These results were analyzed in terms of the perceptual conflict between primary perception and secondary perception.     

The importance of a visual horizon for distance judgments under severely degraded vision

In two experiments we examined the role of visual horizon information on absolute egocentric distance judgments to on-ground targets. Sedgwick [1983, in Human and Machine Vision (New York: Academic Press) pp 425-458] suggested that the visual system may utilize the angle of declination from a horizontal line of sight to the target location (horizon distance relation) to determine absolute distances on infinite ground surfaces. While studies have supported this hypothesis, less is known about the specific cues (vestibular, visual) used to determine horizontal line of sight. We investigated this question by requiring observers to judge distances under degraded vision given an unaltered or raised visual horizon. The results suggest that visual horizon information does influence perception of absolute distances as evident through two different action-based measures: walking or throwing without vision to previously viewed targets. Distances were judged as shorter in the presence of a raised visual horizon. The results are discussed with respect to how the visual system accurately determines absolute distance to objects on a finite ground plane and for their implications for understanding space perception in low-vision individuals.     

More than just perception–action recalibration: Walking through a virtual environment causes rescaling of perceived space

Egocentric distances in virtual environments are commonly underperceived by up to 50 % of the intended distance. However, a brief period of interaction in which participants walk through the virtual environment while receiving visual feedback can dramatically improve distance judgments. Two experiments were designed to explore whether the increase in postinteraction distance judgments is due to perception–action recalibration or the rescaling of perceived space. Perception–action recalibration as a result of walking interaction should only affect action-specific distance judgments, whereas rescaling of perceived space should affect all distance judgments based on the rescaled percept. Participants made blind-walking distance judgments and verbal size judgments in response to objects in a virtual environment before and after interacting with the environment through either walking (Experiment 1) or reaching (Experiment 2). Size judgments were used to infer perceived distance under the assumption of size–distance invariance, and these served as an implicit measure of perceived distance. Preinteraction walking and size-based distance judgments indicated an underperception of egocentric distance, whereas postinteraction walking and size-based distance judgments both increased as a result of the walking interaction, indicating that walking through the virtual environment with continuous visual feedback caused rescaling of the perceived space. However, interaction with the virtual environment through reaching had no effect on either type of distance judgment, indicating that physical translation through the virtual environment may be necessary for a rescaling of perceived space. Furthermore, the size-based distance and walking distance judgments were highly correlated, even across changes in perceived distance, providing support for the size–distance invariance hypothesis.     

Misperception of exocentric directions in auditory space

Previous studies have demonstrated large errors (over 30 degrees ) in visually perceived exocentric directions (the direction between two objects that are both displaced from the observer's location; e.g., Philbeck et al. [Philbeck, J. W., Sargent, J., Arthur, J. C., & Dopkins, S. (2008). Large manual pointing errors, but accurate verbal reports, for indications of target azimuth. Perception, 37, 511-534]). Here, we investigated whether a similar pattern occurs in auditory space. Blindfolded participants either attempted to aim a pointer at auditory targets (an exocentric task) or gave a verbal estimate of the egocentric target azimuth. Targets were located at 20-160 degrees azimuth in the right hemispace. For comparison, we also collected pointing and verbal judgments for visual targets. We found that exocentric pointing responses exhibited sizeable undershooting errors, for both auditory and visual targets, that tended to become more strongly negative as azimuth increased (up to -19 degrees for visual targets at 160 degrees ). Verbal estimates of the auditory and visual target azimuths, however, showed a dramatically different pattern, with relatively small overestimations of azimuths in the rear hemispace. At least some of the differences between verbal and pointing responses appear to be due to the frames of reference underlying the responses; when participants used the pointer to reproduce the egocentric target azimuth rather than the exocentric target direction relative to the pointer, the pattern of pointing errors more closely resembled that seen in verbal reports. These results show that there are similar distortions in perceiving exocentric directions in visual and auditory space.     

Visual perception and the guidance of locomotion without vision to previously seen targets

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.     

Prevalence-based decisions undermine visual search

In visual search, observers make decisions about the presence or absence of a target based on their perception of a target during search. The present study investigated whether decisions can be based on observers’ expectation rather than perception of a target. In Experiment 1, participants were allowed to make target-present responses by clicking on the target or, if the target was not perceived, a target-present button. Participants used the target-present button option more frequently in difficult search trials and when target prevalence was high. Experiment 2 and 3 employed a difficult search task that encouraged the use of prevalence-based decisions. Target presence was reported faster when target prevalence was high, indicating that decisions were, in part, cognitive, and not strictly perceptual. A similar pattern of responses were made even when no targets appeared in the search (Experiment 3). The implication of these prevalence-based decisions for visual search models is discussed.     

Dissociation between visual perception of allocentric distance and visually directed walking of its extent

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.     

Auditory attention causes visual inattentional blindness

When engaged in a visual task, we can fail to detect unexpected events that would otherwise be very noticeable. Here we ask whether a common auditory task, such as that of attending to a verbal stream, can also make us blind to the presence of visual objects that we do not anticipate. In two experiments, one hundred and twenty observers watched a dynamic display while performing either a visual or an auditory attention task, or both simultaneously. When observers were listening to verbal material, in order to either understand it or to remember it (auditory task), their probability of detecting an unexpected visual object was no higher than when they were counting bounces of moving items (visual task), although in the former case the observers' eyes and attention could move around the display freely rather than remaining focused on tracked items. Previous research has shown that attending to verbal material does not affect responses to lights flashing at irregular intervals, suggesting that driving performance is not hampered by listening. The lights, however, were expected. Our data imply that listening to the radio while driving, or to a portable audio player while walking or biking, can impair our reactions to objects or events that we do not expect.     

A comparison of visual and nonvisual sensory inputs to walked distance in a blind-walking task

Two experiments were conducted in order to assess the contribution of locomotor information to estimates of egocentric distance in a walking task. In the first experiment, participants were either shown, or led blind to, a target located at a distance ranging from 4 to 10 m and were then asked to indicate the distance to the target by walking to the location previously occupied by the target. Participants in both the visual and locomotor conditions were very accurate in this task and there was no significant difference between conditions. In the second experiment, a cue-conflict paradigm was used in which, without the knowledge of the participants, the visual and locomotor targets (the targets they were asked to walk to) were at two different distances. Most participants did not notice the conflict, but despite this their responses showed evidence that they had averaged the visual and locomotor inputs to arrive at a walked estimate of distance. Together, these experiments demonstrate that, although they showed poor awareness of their position in space without vision, in some conditions participants were able to use such nonvisual information to arrive at distance estimates as accurate as those given by vision.     

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.     

The effect of perceived locomotor constraints on distance estimation

Two experiments were conducted to examine the ways in which the visual estimation of distance to a target is affected by constraints perceived to be placed on the subsequent locomotion to the target without vision. We hypothesized that an appraisal of impending effort would play a role in ascertaining the distance to be walked. In Experiment 1, the amount of resistance to walking was variable and unpredictable. One group of subjects performed against relatively low resistance, whereas another group performed against substantially greater resistance. In the low-resistance condition, no significant differences in CE, VE, time to target, or number of steps to target were found between any of the eight combinations of predictable or unpredictable resistances during walking. In the high-resistance condition, however, significant differences were found for CE and number of strides to target when resistance varied unpredictably during walking. Experiment 2 was similar in design but required subjects to walk with combinations of normal or short steps after they had viewed the target knowing only the gait type that would be used to begin locomotion. No differences in CE, VE, or time to target were found between four different combinations of gait type and predictability, under subjectively controlled conditions. When the step constraints were externally imposed, however, differences were found for CE. None of the results from either experiment, in which the number of strides needed to reach the target or the predictability of gait did not change from normal, supported the hypothesis that motor output requirements are necessary in forming a mental representation of the target position that can be used to walk to the target with eyes closed. Whichever locomotor technique was used to walk the estimated distance in these cases, the representation was able to be used independently. When walking mechanics were altered by externally imposed constraints, however, the success at reaching the estimated target position was reduced. These latter results are consistent with those obtained using up, down, and level walking and support the premise that mental representations used in blind walking are linked to the locomotor mechanics afforded by environmental conditions.     

The perception of size and distance under monocular observation

A relative-perceived-size hypothesis is proposed to account for the perception of size and distance under monocular observation in reduced-cue settings. This hypothesis is based on two assumptions. In primary processing, perceived size is determined by both proximal stimulation on the retina and distance information from primary cues such as oculomotor cues. In secondary processing, the relation of two primary perceived sizes determines another relation of secondary perceived distances, so that an object of smaller primary perceived size is judged to be further away. An experiment was designed to test this hypothesis, especially the assumption of secondary processing, by making ratio judgments of perceived size and perceived distance for two successively presented targets. The Standard square was presented at a constant distance and varied in visual angle; the variable square was presented with a constant visual angle in distance. The results showed that an inverse relation between size and distance estimates held regardless of whether the visual angles of the targets were the same or different.     

Visually perceived location is an invariant in the control of action

We provide experimental evidence that perceived location is an invariant in the control of action, by showing that different actions are directed toward a single visually specified location in space (corresponding to the putative perceived location) and that this single location, although specified by a fixed physical target, varies with the availability of information about the distance of that target. Observers in two conditions varying in the availability of egocentric distance cues viewed targets at 1.5, 3.1, or 6.0 m and then attempted to walk to the target with eyes closed using one of three paths; the path was not specified until after vision was occluded. The observers stopped at about the same location regardless of the path taken, providing evidence that action was being controlled by some invariant, ostensibly visually perceived location. That it was indeed perceived location was indicated by the manipulation of information about target distance—the trajectories in the full-cues condition converged near the physical target locations, whereas those in the reduced-cues condition converged at locations consistent with the usual perceptual errors found when distance cues are impoverished.     

Visually directed walking to briefly glimpsed targets is not biased toward fixation location

When observers indicate the magnitude of a previously viewed spatial extent by walking without vision to each endpoint, there is little evidence of the perceptual collapse in depth associated with some other methods (e.g. visual matching). One explanation is that both walking and matching are perceptually mediated, but that the perceived layout is task-dependent. In this view, perceived depth beyond 2-3 m is typically distorted by an equidistance effect, whereby the egocentric distances of nonfixated portions of the depth interval are perceptually pulled toward the fixated point. Action-based responses, however, recruit processes that enhance perceptual accuracy as the stimulus configuration is inspected. This predicts that walked indications of egocentric distance performed without vision should exhibit equidistance effects at short exposure durations, but become more accurate at longer exposures. In this paper, two experiments demonstrate that in a well-lit environment there is substantial perceptual anisotropy at near distances (3-5 m), but that walked indications of egocentric distance are quite accurate after brief glimpses (150 ms), even when the walking target is not directly fixated. Longer exposures do not increase accuracy. The results are clearly inconsistent with the task-dependent information processing explanation, but do not rule out others in which perception mediates both walking and visual matches.     

Contribution of extraretinal signals to the scaling of object distance during self-motion

We investigated the role of extraretinal information in the perception of absolute distance. In a computer-simulated environment, monocular observers judged the distance of objects positioned at different locations in depth while performing frontoparallel movements of the head. The objects were spheres covered with random dots subtending three different visual angles. Observers viewed the objects ateye level, either in isolation or superimposed on a ground floor. The distance and size of the spheres were covaried to suppress relative size information. Hence, the main cues to distance were the motion parallax and the extraretinal signals. In three experiments, we found evidence that (1) perceived distance is correlated with simulated distance in terms of precision and accuracy, (2) the accuracy in the distance estimate is slightly improved by the presence of a ground-floor surface, (3) the perceived distance is not altered significantly when the visual field size increases, and (4) the absolute distance is estimated correctly during self-motion. Conversely, stationary subjects failed to report absolute distance when they passively observed a moving object producing the same retinal stimulation, unless they could rely on knowledge of the three-dimensional movements.     

The Effect of Perceived Locomotor Constraints on Distance Estimation

Two experiments were conducted to examine the ways in which the visual estimation of distance to a target is affected by constraints perceived to be placed on the subsequent locomotion to the target without vision. We hypothesized that an appraisal of impending effort would play a role in ascertaining the distance to be walked. In Experiment 1, the amount of resistance to walking was variable and unpredictable. One group of subjects performed against relatively low resistance, whereas another group performed against substantially greater resistance. In the low-resistance condition, no significant differences in CE, VE, time to target, or number of steps to target were found between any of the eight combinations of predictable or unpredictable resistances during walking. In the high-resistance condition, however, significant differences were found for CE and number of strides to target when resistance varied unpredictably during walking. Experiment 2 was similar in design but required subjects to walk with combinations of normal or short steps after they had viewed the target knowing only the gait type that would be used to begin locomotion. No differences in CE, VE, or time to target were found between four different combinations of gait type and predictability, under subjectively controlled conditions. When the step constraints were externally imposed, however, differences were found for CE. None of the results from either experiment, in which the number of strides needed to reach the target or the predictability of gait did not change from normal, supported the hypothesis that motor output requirements are necessary in forming a mental representation of the target position that can be used to walk to the target with eyes closed. Whichever locomotor technique was used to walk the estimated distance in these cases, the representation was able to be used independently. When walking mechanics were altered by externally imposed constraints, however, the success at reaching the estimated target position was reduced. These latter results are consistent with those obtained using up, down, and level walking and support the premise that mental representations used in blind walking are linked to the locomotor mechanics afforded by environmental conditions.     

Cross-modal exogenous attention and distance effects in vision and hearing

In the present study we investigated cross-modal orienting in vision and hearing by using a cueing task with four different horizontal locations. Our main interest concerned cue–target distance effects, which might further our insight in the characteristics of cross-modal spatial attention mechanisms. A very consistent pattern was observed for both the unimodal (cue and target were both visual or auditory) and the cross-modal conditions (cue and target from different modalities). RTs to valid trials were faster than for invalid trials, and, most interestingly, there was a distance effect: RTs increased with greater cue–target distance. This applied to detection of visual targets and to localisation of both visual and auditory targets. The time interval between cue and target was also varied. Surprisingly, there was no indication of inhibition of return even with the longest cue–target intervals. In order to assess the role of endogenous (strategic) factors in exogenous spatial attention we increased in two additional experiments the cue validity from 25% to 80%. This appeared to have no large influence on the cueing pattern in both the detection and localisation tasks. Currently, it is assumed that spatial attention is organised in multiple strongly linked modality-specific systems. The foregoing results are discussed with respect to this supposed organisation.     

Is it really too far? Overestimating walk time and distance reduces walking

In this paper we use an intercept survey of 1,297 people at seven locations in New Jersey to answer three questions about perceived distances and walk times to nearby destinations. First, we seek to clarify conflicting results from the literature by asking: what factors are associated with perceived distance and walk times? Like other studies, we find that people overestimate both walk times and distances. We find that characteristics of the route matter. People are more likely to overestimate in car-dependent locations, along routes with many turns or barriers, or for destinations that are relatively closer. In terms of personal characteristics, experience walking and familiarity with the area both lead to lower estimates, while concerns about crime, getting lost, or carrying something heavy increase estimates. Next, we explore whether overestimating walk times and distances reduces the likelihood of walking. We find that people who overestimate are less likely to walk, everything else equal. Together, these results suggest that wayfinding campaigns that clarify the travel time to nearby destinations and ease the fear of getting lost are likely to improve perceptions and increase walking. We make an additional contribution by highlighting important differences between our university and town center samples, which raises questions about the reliance on student samples in research.     

The way the ball bounces: visual and auditory perception of elasticity and control of the bounce pass

Human observers may perceive not only spatial and temporal dimensions of the environment, but also dynamic physical properties that are useful for the control of behavior. A study is presented in which visual and auditory perception of elasticity in bouncing objects, which was specified by kinematic (spatiotemporal) patterns of object motion, were examined. In experiment 1, observers could perceive the elasticity of a bouncing ball and were able to regulate the impulse applied to the ball in a bounce pass. In experiments 2 and 3, it was demonstrated that visual perception of elasticity was based on relative height information, when it was available, and on the duration of a single period under other conditions. Observers did not make effective use of velocity information. In experiment 4, visual and auditory period information were compared and equivalent performance in both modalities was found. The results are interpreted as support for the view that dynamic properties of environmental events are perceived by means of kinematic information.