Assessing auditory distance perception using perceptually directed action

Three experiments investigated auditory distance perception under natural listening conditions in a large open field. Targets varied in egocentric distance from 3 to 16 m. By presenting visual targets at these same locations on other trials, we were able to compare visual and auditory distance perception under similar circumstances. In some experimental conditions, observers made verbal reports of target distance. In others, observers viewed or listened to the target and then, without further perceptual information about the target, attempted to face the target, walk directly to it, or walk along a two-segment indirect path to it. The primary results were these. First, the verbal and walking responses were largely concordant, with the walking responses exhibiting less between-observer variability. Second, different motoric responses provided consistent estimates of the perceived target locations and, therefore, of the initially perceived distances. Third, under circumstances for which visual targets were perceived more or less correctly in distance using the more precise walking response, auditory targets were generally perceived with considerable systematic error. In particular, the perceived locations of the auditory targets varied only about half as much in distance as did the physical targets; in addition, there was a tendency to underestimate target distance, except for the closest targets.     

Progressive locomotor recalibration during blind walking

Blind walking has become a common measure of perceived target location. This article addresses the possibility that blind walking might vary systematically within an experimental session as participants accrue exposure to nonvisual locomotion. Such variations could complicate the interpretation of blind walking as a measure of perceived location. We measured walked distance, velocity, and pace length in indoor and outdoor environments (1.5-16.0 m target distances). Walked distance increased over 37 trials by approximately 9.33% of the target distance; velocity (and to a lesser extent, pace length) also increased, primarily in the first few trials. In addition, participants exhibited more unintentional forward drift in a blindfolded marching-in-place task after exposure to nonvisual walking. The results suggest that participants not only gain confidence as blind-walking exposure increases, but also adapt to nonvisual walking in a way that biases responses toward progressively longer walked distances.     

Updating of locations during whole-body rotations in patients with hemispatial neglect

Posterior parietal cortex lesions have been associated with both hemispatial neglect and spatialupdating deficits. Currently, the relation between these processes remains poorly understood. We tested the ability of parietal patients with neglect to update remembered target locations during passive whole-body rotations. The rotations and manual pointing responses were executed with and without vision. During the rotation, the remembered location stayed on the same side of the body midline or crossed the midline. Parietal patients generally underestimated rotations, as compared with control groups, but updated targets equally well on either side of the body midline, regardless of the amount of updating required. Once parietal patients have localized a target, they can use self-motion information to update its location, even if it passes into the region they typically neglect. This lack of contralesional updating effects contrasts with impairments in eye position updating found in previous work with parietal patients.     

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.