Time-To-Contact Judgements Based on Haptic Information
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The use of visual optical time-to-contact information (an optical variable Lee (1980) designated as tau) in control of action has been explored in a variety of contexts over the years (for an overview, see Savelsbergh & Chen, 1993, and Savelsbergh, 1990). Although a majority of the experiments reported have been in the visual mode, note should be taken of Fitch, Tuller, and Turvey's (1982) point "that the information needed to tune muscle systems is not tied to a particular sense modality" (p. 277). Rosenblum, Carello and Pastore (1987), like Schiff and Oldak (1990), demonstrated that subjects can make reliable judgements about the timing of a moving sound source. An experiment on vision substitution devices for the blind conducted by White and his co-workers showed that a matrix of vibrations acts as a "tactile" array (White, Saunders, Scadden, Bach-y-Rita, & Collins, 1970). In this experiment one vision substitution system transmitted a pattern of intensity differences from a portable television camera to a bank of mechanical vibrators on the subject's back. This matrix of vibrators acts like a tactile array, which can be made to change by the optical array as presented by a camera. While testing this device, the experimenter accidentally moved the zoom lens. This resulted in a rapidly expanding tactile array on the back of the subject which was followed by an avoidance reaction on his part. The expanding tactile array, like an expanding optic array, specified that an object was about to make contact.