Mentally retarded and nonretarded adults' sensitivity to spatial structure.

The sensitivity of mentally retarded and nonretarded adults to changes in the structure of their perspectives when those changes are occluded from view during a walk was examined in two studies. Sensitivity was tested by starting participants at a target object located in one room of an unfamiliar office building, walking them via a circuitous path into a new room from which the target was occluded from view, and then asking them to aim a pointer straight at it. Direction judgments were collected across variations in the number of turns in the walk, spatial arrangements of rooms, amount of the subjects' attention available during the walk, and the availability of visual-environmental cues. Results indicate that retarded and nonretarded persons show similar levels of sensitivity to changes in perspective when they walk without visual-environmental cues (i.e., with eyes closed). In the presence of visual-environmental cues, however, the accuracy of nonretarded subjects increased dramatically whereas the retarded subjects did not improve at all. The similarities and differences in performance are related to differences in the perceptual learning thought to mediate use of proprioceptive cues and the inferential processes thought to mediate use of visual-environmental cues.

Sensitivity to perspective structure while walking without vision.

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.