The identification of the direction of electrocutaneous stimulation along lineal multistimulator arrays

The generation of vibrotactile patterns on a linear array: influences of body site, time, and presentation mode

In order to provide information regarding orientation or direction, a convenient code employs vectors (lines) because they have both length and direction. Potential users of such information, encoded tactually, could include persons who are blind, as well as pilots, astronauts, and scuba divers, all of whom need to maintain spatial awareness in their respective unusual environments. In these situations, a tactile display can enhance environmental awareness. In this study, optimal parameters were explored for lines presented dynamically to the skin with vibrotactile arrays on three body sites, with veridical and saltatory presentation modes. Perceived length, straightness, spatial distribution, and smoothness were judged while the durations of the discrete taps making up the "drawn" dotted lines and the times between them were varied. The results indicate that the two modes produce equivalent sensations and that similar sets of timing parameters, within the ranges tested, result in "good" lines at each site.

Localization of electrocutaneous stimuli on the fingers and forearm: effects of electrode configuration and body axis

Four experiments were done on the effects of electrode configuration (concentric vs. unifocal) and body axis (longitudinal vs. transverse) on localization of electrocutaneous pulse stimuli at the fingers and forearm. Subjects pointed to the apparent location of current pulses. For the transverse placement of electrodes, pulses were localized correctly, whatever the configuration and the body site might be. In addition, intrasubject variability at the forearm was smaller for the transverse axis than for the longitudinal axis. For the longitudinal placement of electrodes, pulses were localized as a function of configuration and body site. At the fingers, concentric electrodes provided precise localization but unifocal electrodes provided a great mislocalization; and intrasubject variability of localization was larger for the unifocal electrodes than for the concentric electrodes. At the forearm, whatever the configuration might be, the pulses were localized more proximally than the stimulus site; and intrasubject variability of localization did not differ between the configurations. These results are related to Boring's anchor theory, apparent distance between two points, and the localization of other somatosensory stimuli.

Electrotactile and vibrotactile displays for sensory substitution systems

Sensory substitution systems provide their users with environmental information through a human sensory channel (eye, ear, or skin) different from that normally used, or with the information processed in some useful way. We review the methods used to present visual, auditory, and modified tactile information to the skin. First, we discuss present and potential future applications of sensory substitution, including tactile vision substitution (TVS), tactile auditory substitution, and remote tactile sensing or feedback (teletouch). Next, we review the relevant sensory physiology of the skin, including both the mechanisms of normal touch and the mechanisms and sensations associated with electrical stimulation of the skin using surface electrodes (electrotactile (also called electrocutaneous) stimulation). We briefly summarize the information-processing ability of the tactile sense and its relevance to sensory substitution. Finally, we discuss the limitations of current tactile display technologies and suggest areas requiring further research for sensory substitution systems to become more practical.

Tactual perception of speech-like stimuli with an electrocutaneous vocoder

A deficiency in current tactual vocoder designs is the relatively poor transmission of rapid spectral changes (formant transitions). To understand better the application of electrocutaneous tactual stimulation as a basis for an artificial hearing system, the tactual discrimination of rapidly changing patterns was studied. Stimuli were presented on a belt containing 32 electrodes that was worn in a linear array 5 cm above the navel. Bipolar pulse trains (height 10 mA; width 13 microseconds) of specified frequencies (200, 400, or 1,000 Hz) were presented sequentially to adjacent electrodes to simulate a tactual vocoder equivalent of simple frequency transitions. Discrimination of the direction of stimulation movement (i.e., stimulation on the belt to either a subject's left or right) was assessed with one experienced subject as a function of both electrode number (four or eight electrodes) and stimulation frequency. Identification of the direction of stimulation movement was influenced both by the number of stimulus channels and by the frequency of electrocutaneous stimulation. These preliminary results indicate that the discrimination of formant trajectory transmitted in an electrocutaneous vocoder scheme is within the temporal limits typically imposed by natural speech.