Research on the visual information used in collision avoidance has inappropriately attributed adequate task performance to the use of the visual variable tau (τ). We constructed a collision avoidance experiment where the τ hypothesis was tested against the use of other potential information sources, including expansion rate. Subjects viewed a head-on flight towards one or two barriers. During the first half of trials, a single barrier was present and subjects were instructed to approach it as closely as possible before ascending over it. During the second half of the trials, a second barrier was placed above the first and subjects flew through the resulting gap. The ascent dynamics were manipulated between subjects, such that a time-to-contact margin demarcated the collision boundary with one group, but a constant distance-to-contact margin with another group. Subjects in the time-relevant group responded in a manner more consistent with the use of expansion rate information, but neither a single critical expansion rate or τ strategy adequately explains performance in the two-barrier condition. Subjects in the distance-relevant group responded in a manner consistent with the use of relative distance information.
Control a Redundant Robot Using Visual Information. Avoidance Control of a Moving Obstacle.