Abstract
This study examined how visual and nonvisual cues are integrated in a distance estimation task by systematically varying cue availability. Distance stimuli were presented in one of three modes: by traversing a distance blindfolded (traversed distance — TD), by traversing a distance with optic flow (TDO), or by visually previewing a target distance from a static location (VPD). Distance estimates were then produced in one of the three modes in which the stimuli were presented. Each of these stimulus modes was paired with each of the three response modes and each subject experienced all combinations. Stimuli were presented in one direction and subjects turned 180 deg. before producing their estimates. Experiments were conducted in a large-scale, open, outdoor environment. During conditions in which the stimulus and response were delivered in the same mode (TD or VPD), when optic flow was absent, constant error was minimal, whereas when optic flow was present (TDO), overestimation was observed. In conditions in which the stimulus and response modes differed, the pattern of responding depended on whether or not optic flow was available. When optic flow was absent, if the stimulus was presented as a VPD and reported via TD (blind walking task), underestimation was observed. However, if the stimulus and response modes were reversed, overestimation was observed. In contrast, when optic flow was present, the opposite results were observed such that, if the stimulus was presented as a VPD and reported via TDO, overestimation was observed and if the stimulus and response modes were reversed, underestimation was observed. These results demonstrate that when optic flow is present in the response phase, overestimation occurs. Overall, the magnitude of error observed in conditions without optic flow was reasonably low, whereas errors in conditions with optic flow suggest that continuous visual monitoring does not necessarily enhance the accuracy of distance estimation.