Abstract
It has been clearly demonstrated that humans are able to visually assess a target distance and accurately match that distance through blindfolded locomotion. In comparison, relatively little is known regarding the relative contributions of dynamic visual information and locomotor information when both are available simultaneously in a natural, cue-rich environment. Previous results have suggested that the availability of visual information during locomotion, mainly optic flow, leads to an under-perception of movement when compared to situations in which optic flow is absent (Sun et al, Perception, In press). The current experiment was conducted in a large-scale, open, outdoor environment. Subjects were presented with a target distance twice, once via blindfolded locomotion and once via sighted locomotion (with the order of the two randomized). For the majority of trials the magnitude of the two distances were the same, but for a small subset of trials the two distances differed in magnitude. Following the two distance presentations, subjects were required to produce a distance estimate via blindfolded locomotion. Results indicate that both the type of cues and the order in which the cues were presented, affected subjects' distance estimations. For all congruent trials, when the second stimulus presentation involved sighted locomotion, subjects estimated the distance to be longer than trials in which the second stimulus presentation involved blindfolded locomotion. For incongruent trials, although the pattern mirrored that of the congruent trials, there was also an effect of distance discrepancy, such that when the longer of the two distances was presented second, distance estimates were greater, whereas when the shorter of the two distances was presented second, distance estimates were less. The results were explained in terms of a linear model using a weighted average of distance cues and distance presentation order.
