Kurt A. Kaczmarek

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. The authors review the methods used to present visual, auditory, and modified tactile information to the skin and discuss present and potential future applications of sensory substitution, including tactile vision substitution (TVS), tactile auditory substitution, and remote tactile sensing or feedback (teletouch). The relevant sensory physiology of the skin, including the mechanisms of normal touch and the mechanisms and sensations associated with electrical stimulation of the skin using surface electrodes (electrotactile, or electrocutaneous, stimulation), is reviewed. The information-processing ability of the tactile sense and its relevance to sensory substitution is briefly summarized. The limitations of current tactile display technologies are discussed, and areas requiring further research for sensory substitution systems to become more practical are suggested.<<ETX>>

Seeing with the Brain

We see with the brain, not the eyes (Bach-y-Rita, 1972); images that pass through our pupils go no further than the retina. From there image information travels to the rest of the brain by means of coded pulse trains, and the brain, being highly plastic, can learn to interpret them in visual terms. Perceptual levels of the brain interpret the spatially encoded neural activity, modified and augmented by nonsynaptic and other brain plasticity mechanisms (Bach-y-Rita, 1972, 1995, 1999, in press). However, the cognitive value of that information is not merely a process of image analysis. Perception of the image relies on memory, learning, contextual interpretation (e.g., we perceive intent of the driver in the slight lateral movements of a car in front of us on the highway), cultural, and other social factors that are probably exclusively human characteristics that provide “qualia” (Bach-y-Rita, 1996b). This is the basis for our tactile vision substitution system (TVSS) studies that, starting in 1963, have demonstrated that visual information and the subjective qualities of seeing can be obtained tactually using sensory substitution systems.1 The description of studies with this system have been taken INTERNATIONAL JOURNAL OF HUMAN–COMPUTER INTERACTION, 15(2), 285–295 Copyright

Polarity Effect in Electrovibration for Tactile Display

Electrovibration is the tactile sensation of an alternating potential between the human body and a smooth conducting surface when the skin slides over the surface and where the current is too small to stimulate sensory nerves directly. It has been proposed as a high-density tactile display method, for example to display pictographic information to persons who are blind. Previous models for the electrovibration transduction mechanism are based on a parallel-plate capacitor in which the electrostatic force is insensitive to polarity. We present experimental data showing that electrovibratory perceptual sensitivity to positive pulses is less than that for negative or biphasic pulses and propose that this disparity may be due to the asymmetric electrical properties of human skin. We furthermore propose using negative pulses for insulated tactile displays based on electrovibration because their sensory thresholds were found to be more stable than for waveforms incorporating positive pulses

Comparison of human sensory capabilities with technical specifications of virtual environment equipment

This paper presents the results of three surveys that compared the humans ability to detect and discriminate visual, auditory, tactile, and kinesthetic information with current technical specifications of virtual environment equipment. The comparison exposes limitations of current virtual environment interfaces and thus indicates areas where improvements in equipment design are needed. Furthermore, the paper presents basic definitions and units of measurement for sensory modalities, which also can be used to describe the capabilities of virtual environment equipment. Finally, the paper concludes with remarks concerning the relationship between the data presented in the three surveys and the design of virtual interfaces.

Electrotactile haptic display on the fingertips: preliminary results

Electrical stimulation of the sense of touch may be used to display pictorial information to blind computer users via a fingertip-scanned (haptic) touch tablet containing embedded electrodes. This might be particularly useful to users of systems with graphical user interfaces, or with drawing and layout software. Electrotactile (electrocutaneous) stimulation on the fingertip, however, differs substantially from that on other body locations. We discuss the implications of designing a practical graphics haptic display by addressing the high-resistance and variable nature of the fingertip electrode-skin interface.<<ETX>>

Maximal dynamic range electrotactile stimulation waveforms

A new method to measure the dynamic range of electrotactile (electrocutaneous) stimulation uses both steepest ascent (gradient) and one-variable-at-a-time methods to determine the waveform variables that maximize the subjective magnitude (intensity) of the electrotactile percept at the maximal current without discomfort for balanced-biphasic pulse bursts presented at a 15-Hz rate. The magnitude at the maximal current without discomfort is maximized by the following waveform (range tested in parenthesis): number of pulses/burst=6 (1-20), pulse repetition rate within a burst=350 Hz (200-1500), and phase width=150 mu s (40-350). The interphase interval (separation between positive and negative phases in a biphasic pulse) does not affect dynamic range from 0-500 mu s. The number of pulses/burst has a large effect on the perceived dynamic range when this is measured using a subjective-magnitude-based algorithm, whereas it has little effect on the traditional dynamic range measure, i.e., (maximal current without discomfort)/(sensation threshold current).<<ETX>>

Pattern identification and perceived stimulus quality as a function of stimulation waveform on a fingertip-scanned electrotactile display

The effect of stimulation waveform on pattern perception was investigated on a 49-point fingertip-scanned electrotactile (electrocutaneous) display. Waveform variables burst frequency (F), number of pulses per burst (NPB), and pulse repetition rate (PRR) were varied in a factorial design. Contrast reduction was used to limit performance of perceiving a 1-tactor gap defined within a 3 /spl times/ 3 tactor outline square. All three variables accounted for significant variations in performance with higher levels of F and NPB and lower levels of PRR, leading to better performance. In addition, we collected qualitative data on each waveform, and the qualitative differences were related to performance (e.g., waveforms perceived as having a more localized sensation were correlated with better pattern identification performance than those waveforms perceived as more broad). We also investigated the effect of stimulation contrast on pattern perception.

Electrotactile adaptation on the abdomen: preliminary results

Electrotactile (electrocutaneous) stimulation at currents greater than sensation threshold causes sensory adaptation, which temporarily raises the sensation threshold and reduces the perceived magnitude of stimulation. After 15 min of moderately intense exposure to a conditioning stimulus (10 s on, 10 s off), the sensation threshold elevation for seven observers was 60-270%, depending on the current, frequency, and number of pulses in the burst structure of the conditioning stimulus. Increases in any of these parameters increased the sensation threshold elevation. Adaptation and recovery were each complete in approximately 15 min.

A 16-channel 8-parameter waveform electrotactile stimulation system

A general-purpose electrotactile (electrocutaneous) stimulation system has been developed as a research tool for studying psychophysiological performance associated with various stimulation waveforms. An experimenter-defined command file specifies the stimulation current and waveform of each of the 16 channels. The system provides a burst onset delay of 0-20 ms, a phase current of 0-50 mA, an interphase interval of 0-1000 mu s, 1-100 pulses per burst, a pulse repetition rate of 0.1-25 kHz, a phase width of 2-1000 mu s, and functionally monophasic pulses (with zero DC current) or balanced-biphasic pulses (with equal positive and negative phases). The system automatically delivers the desired stimulation, prompts the subject for responses, and then logs subject responses. Key features of the system are (1) the very flexible choice of bursts of pulsatile waveforms, (2) the real-time control of all of the waveform parameters as mathematical functions of external analog inputs, and (3) the high-performance electrode-driver circuitry.<<ETX>>

A Tactile Vision-Substitution System for the Blind: Computer-Controlled Partial Image Sequencing

We have developed a computer-controlled tactile vision-substitution system as part of a study to maximize the use of the skins ability to process spatial and temporal information. The system receives a 128-column × 64-row image from a commercially available digital camera. An IBM personal computer sections the image into a controllable number of 6 × 24 blocks. The computer then sequentially sends these blocks to the 6 × 24 vibratory fingertip stimulation matrix on an Optacon reading device for the blind. Custom hardware provides the interface between the IBM PC and the Optacon. The image manipulation software is written in Intel 8088 assembly code.