Haptic distal spatial perception mediated by strings: point of closest approach and bypass distance

Four experiments examined haptic perception of two distal spatial properties in a bypass event. A hook suspended a string held taut between the participant's finger and a weight. Moving their fingers laterally beneath the hook, participants estimated the finger's point of closest approach (PCA) to the hook and bypass distance (BPD; i.e., hook height above the finger's track at PCA). Experiment 1 yielded near perfect PCA estimates (group average r > .99), independent of BPD and traverse distance. Experiment 2 replicated PCA results, and showed good BPD estimates (group r = .74). BPD estimates depended on lateral movement distance to PCA, but not weight. In Experiment 3, feedback on accuracy improved BPD estimates (maximum group average R = .91). Magnitude estimation of BPD in Experiment 4 yielded a power law relationship (group average r = .90; exponent, .30). Results show that human perceivers can make effective judgments of PCA and BPD using haptically available force relationships. Results are interpreted in terms of haptics as a telemodality, the Gibsonian perceptual research program, and dynamic touch.