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.