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Abstract: Information Transmission with a Multi-finger Tactual Display

Information Transmission with a Multi-finger Tactual Display

Hong Z. Tan
Nathaniel I. Durlach
William M. Rabinowitz
Charlotte M. Reed

Proceedings of International Sensory Aid Conference, May 28-31, Sint-Michielsgestel, The Netherlands

© 1996 ISAC. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale, or to reuse any copyrighted component of this work in other works must be obtained from the International Sensory Aid Conference.

Abstract:

Motivated by the highly successful Tadoma method of speech communication, a multi-finger positional display (the Tactuator) was developed to study perception via the kinesthetic and vibrotactile aspects of the tactual sensory system of the hand. The display consists of three independent single contact-point actuators interfaced (individually) with the fingerpads of the thumb, the index finger, and the middle finger. Arbitrary stimulus waveforms from absolute detection threshold to about 50 dB SL throughout the frequency range from near DC to above 300 Hz can be delivered to the three digits simultaneously (e.g., 25-mm low-frequency motion with superimposed high-frequency vibration). Absolute thresholds measured with the stimulator are in general agreement with results from the literature.

The information transmission capabilities with the Tactuator were assessed through a series of absolute identification experiments. Test signals were derived by varying frequency and amplitude parameters of multicomponent waveforms. Three frequency regions were defined based on their relatively distinct perceptual attributes: smooth motion (up to about 6 Hz), a rough or fluttering sensation (about 10 to 70 Hz), and smooth vibration (above about 150 Hz). Multi-component stimuli were formed by summing sinusoids from each of these three regions, with the intent that frequency and amplitude variations within each region could be identified independently. Stimulation was applied to either one of three digits (thumb, index, or middle) or to all three digits simultaneously. For stimulus durations of 500 and 250 ms, information transfer (IT) was 6.6 bits (corresponding to perfect identification of 97 stimuli); at 125 ms, IT was 6.0 bits. Estimates of potential IT rates were obtained by sequencing three random stimuli and (a) having the subject identify only the middle stimulus and (b) extrapolating this IT to that for continuous streams. Stimulus durations of 125 to 500 ms and presentation rates of 1 to 7 items/sec were tested. Estimated IT rate was about 12 bits/sec, and optimal stimulus presentation rates were between 2 to 3 items/sec independent of stimulus duration. This IT rate is roughly the same as that achieved by Tadoma users in tactual speech communication.

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