Nonvisual navigation by blind and sighted: assessment of path integration ability.

Blindfolded sighted, adventitiously blind, and congenitally blind subjects performed a set of navigation tasks. The more complex tasks involved spatial inference and included retracing a multisegment route in reverse, returning directly to an origin after being led over linear segments, and pointing to targets after locomotion. As a group, subjects responded systematically to route manipulations in the complex tasks, but performance was poor. Patterns of error and response latency are informative about the internal representation used; in particular, they do not support the hypothesis that only a representation of the origin of locomotion is maintained. The slight performance differences between groups varying in visual experience were neither large nor consistent across tasks. Results provide little indication that spatial competence strongly depends on prior visual experience.

Active localization of virtual sounds.

A simple virtual sound display built around a microcomputer and analog hardware is described. The display implements most of the primary cues for sound localization in the ear-level plane. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, it is concluded that simple displays like the one described are effective in creating the impression of external sounds to which observers can locomote with ease; in particular, this means that simulation of the direction-dependent spectral shaping effects of the pinnae is not a necessary requirement for extracranial sound localization.

Acquisition of route and survey knowledge in the absence of vision.

The ability of sighted, blindfolded individuals to navigate while walking was assessed in two types of tasks, one requiring knowledge of a route that previously had been navigated and another requiring more complex spatial inference or computation. A computerized measurement system monitored spatial position. The route tasks included maintenance of a heading, distance and turn reproduction and estimation, and turn production. The inferential task required completion of a multisegment pathway by returning directly to the origin. pathways were replicated at two different scales. Measures for the route-knowledge tasks indicated a substantial ability to navigate in the absence of visual cues. Route reproduction performance was particularly accurate despite intrinsic veering tendencies. A substantial increase in error was observed in the pattern-completion task. Errors in pathway completion increased with pathway complexity and were quite similar in the two scales. Correlational data suggested that performance on different route-knowledge tasks reflected differing underlying representations. The completion task led to a high correlation between absolute turn and distance error but had minimal correlations with the route tasks. The data suggest that a survey representation with some degree of scale independence was constructed for use in the pathway completion task.