Experiments are reported of the nonvisual sensitivity of observers to their paths of locomotion and to the resulting changes in the structure of their perspectives, ie changes in the network of directions and distances spatially relating them to objects fixed in the surrounding environment. In the first experiment it was found that adults can keep up to date on the changing structure of their perspectives even in the absence of sights and sounds that specify changes in self-to-object relations. They do this rapidly, accurately, and, according to the subjects' reports, automatically, as if perceiving the new perspective structures. The second experiment was designed to investigate the role of visual experience in the development of sensitivity to occluded changes in perspective structure by comparing the judgments of sighted adults with those of late-blinded adults (who had extensive life histories of vision) and those of early-blinded adults (who had little or no history of vision). The three groups performed similarly when asked to judge perspective while imagining a new point of observation. However, locomoting to the new point greatly facilitated the judgments of the sighted and late-blinded subjects, but not those of the early-blinded subjects. The findings indicate that visual experience plays an important role in the development of sensitivity to changes in perspective structure when walking without vision.

When places are explored without vision, observers go from temporally sequenced, circuitous inputs available along walks to knowledge of spatial structure (i.e., straight-line distances and directions characterizing the simultaneous arrangement of the objects passed along the way). Studies show that a life history of vision helps develop nonvisual sensitivity, but they are unspecific on the formative experiences or the underlying processes. This study compared judgments of straight-line distances and directions among landmarks in a familiar area of town by partially sighted persons who varied in types and ages of visual impairment. Those with early childhood loss of broad-field vision and those blind from birth performed significantly worse than those with early or late acuity loss and those with late field loss. Broad-field visual experience facilitates perceptual development by providing a basis for proprioceptive and efferent information from locomotion against distances and directions relative to the surrounding environment. Differences in the perception of walking, in turn, cause the observed differences in sensitivity to spatial structure.

The study presented here examined the videotaped search patterns and strategies that 65 persons with visual impairments used to locate and learn the arrangement of five objects in a novel space. Videotapes of the 15 best-performing and 15 worst-performing participants’ explorations were then compared to the participants’ verbal self-reports of the strategies they used. The best-performing participants used search patterns and strategies that were effective in locating objects quickly and that facilitated the development of object-to-object relationships.

The ability to perceive objects from a distance and navigate without vision depends principally on auditory information. Two experiments were conducted in order to assess this ability in congenitally blind children aged 4 to 12 years who had negligible amounts of visual experience or formal mobility training. In Experiment 1, children walked along a sidewalk toward a target location to get some candy. A box was placed along the path on some trials, and the children were instructed to avoid the box if it was present. The children spent more time in the region just in front of the box than in the region just behind it, indicating that they perceived the box and acted 80 as to navigate around it. In Experiment 2, children attempted to discriminate whether a nearby disk was on their left or on their right. The children performed at above-chance levels, again indicating distal perception of objects. fie results of both experiments suggest that blind children with little or no visual experience or formal training utilize-nonvisual information, presumably auditory, to perceive objects. The specific nature of this auditory information requires further investigation, but these findings imply that the underlying perceptual ability does not require experience in spatial vision or deliberate training and intervention.Navigation through cluttered environments depends on perception of the locations of objects and surfaces so that obstacles can be avoided and clear pathways can be used. Although vision is ideally suited for this task, both blind observers and blindfolded sighted observers can locomote without collisions through spaces containing large objects (Supa, Cotzin, & Dallenbach, 1944; Worchel, Mauny, & Andrew, 1950). Various explanatory processes for this ability to navigate without vision have been proposed over the years, including "facial vision" resulting from sensitivity to changes in air pressure near surfaces, a "sixth sense" unique to blind persons, and echolocation based on reflected sounds. The ability is mediated by sensitivity to auditory information, probably in the form of reflected sounds or sound shadows. For example, Supa et al. (1944) found that both blind observers and blindfolded sighted observers who could otherwise stop I-2m in front of a large panel collided with it if their hearing was strongly attenuated. Attenuation of other potential sensory information, such as tactile or thermal stimulation, did not adversely affect performance, so it was concluded that auditory information was necessary and sufficient.

Despite advances in the professional areas of orientation and mobility, processes of spatial learning and orientation are not well understood, and the benefits of existing teaching techniques vary widely from client to client. Wayfinding is mediated by mental processes through which travelers learn the spatial layout of a locale, update their own positions relative to their surroundings, and apply general spatial concepts to particular travel situations. In this article we describe these three components, describe what is well known about each and what we need to know to improve professional practice, and provide a detailed description of three experiments which are focussed on the use of one component (spatial updating) by early-blinded, late-blinded, and sighted adults.

This article reports the results of a study to assess variations in the indoor and outdoor locomotor mobility of 22 low vision adults. Visual acuity, visual field, and contrast sensitivity data were obtained on all participants. Participants were also videotaped while walking unfamiliar indoor and outdoor routes under normal and reduced illumination. These videotapes were viewed by orientation and mobility instructors, who recorded such incidents as stopping or contacting objects during travel. Mobility assessment data obtained from the videotapes were analyzed in relation to type and degree of visual loss. Individuals’ visual fields and contrast sensitivities were found to be related to mobility performance, whereas their visual acuities were not. Visual field and contrast sensitivity together accounted for 39 percent of the variation in mobility performance. Results of the study are discussed in regard to the importance of visual contrast sensitivity and visual field for functional acitivities such as mobility.

This article reports three experiments that assessed pedestrians’ ability to use traffic sounds to establish “alignment,” the initial trajectory of a street crossing. The subjects were well practiced blind adults and unpracticed sighted adults, the dependent variables were variable error and constant error, and the independent variables were the characteristics of traffic and the subjects’ visual experience. The findings document the usefulness of traffic sounds, but show that traffic sounds cannot be used to guarantee accurate alignment. The characteristics of traffic had similar effects on the precision of alignment (variable error) of the blind and sighted subjects, but differentially affected their directional bias (constant error). The implications of the findings for orientation and mobility instructors are discussed.

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