Information from time-varying vibrotactile stimuli

Experiments have been carried out to investigate the information transfer available via a single vibrator on the fingertip. In a first experiment, for stimuli with durations 80 to 320 ms, discrimination of a one- octave step change in frequency at the halfway point was investigated. Results were similar for three stimulus types - sinewave, monophasic pulse and tetraphasic pulse - suggesting temporal cues are more important than spectral cues in this task. In a second experiment, subjects were required to perceive changes in a sequence of stimulus elements. A presentation rate of 6.25 elements s -1 was found to give better results than a rate of 12.5 elements s -1. In the former case, the potential information transfer per element was estimated to be approximately 1.0 bits, corresponding to an information transfer rate of around 6 bits s -1. Implications for the design of a tactile aid to lipreading are discussed.