Vibrotactile Patterns Research Articles

Temporal integration of vibrotactile patterns.

Three experiments were conducted to measure the temporal integration of vibrotactile patterns presented to the fingertip. In Experiment 1, letters were divided in half and the time between the onsets of the first half of the letter and second half of the letter, stimulus onset asynchrony (SOA), was varied. The recognizability of the letters declined as the SOA was increased from 9 to 100 msec. In Experiment 2, the time between two patterns constituting a masking stimulus was varied and the stimulus effectiveness in interfering with letter recognition was determined. The amount of masking increased as the SOA increased from 9 to 50 msec. In Experiment 3, the SOA between a letter and its complement (the portions of the tactile array not activated by the letter) was varied. Increasing SOA from 9 to approximately 50 msec led to increasingly accurate letter recognition. The results of the three experiments suggest that the skin is capable of complete temporal integration over a time period of less than 10 msec, and that the temporal integration function becomes asymptotic in 50 to 100 msec. The results also suggest that the onset of a vibrotactile pattern is critical for generating contours. The implications of the results for modes of generating tactile patterns and for temporal masking functions are discussed.

Tactile letter recognition: pattern duration and modes of pattern generation.

Measurements were made of the ability of subjects to identify vibrotactile patterns presented to their fingertips. The patterns were letters of the alphabet generated on the tactile display of the Optacon. Five different modes of pattern generation were examined. Two of the modes, static and scan, involved full-field presentations of the letters. In the remaining three modes, patterns were generated by presenting parts of the letters sequentially. In one mode, the letters were exposed by a slit passing across them. In the other two modes, the patterns were generated as though the letter were being drawn on the skin. Performance in all five modes was examined as a function of pattern duration, with durations ranging from 4 to 1,000 msec. Increasing duration, up to 400 msec, resulted in generally improved performance, although the functions relating performance and duration differed according to the mode of presentation. Contrary to previous results, the static mode produced the best overall performance level. Some possible reasons for the disagreement between the present results and previous results and some models of cutaneous pattern recognition are discussed.

A computer-controlled matrix system for presentation to the skin of complex spatiotemporal patterns

A system for presenting complex spatiotemporal patterns to the skin is described. The computer-controlled device consists of a matrix of 64 piezoceramic benders mounted in a support system that can be fitted to steeply contoured skin surfaces such as the thigh. Vibrotactile patterns that include movement across the skin’s surface and/or intensitive variation within or across display epochs are programmed and presented in a frame-by-frame manner, similar to the production of motion pictures. Patterns can be predefined, or modified by observers’ responses to allow for an interactive haptographic display. Design considerations for the construction of the tactile matrix, computer interface, and software are discussed.

Interaction of display mode and character size in vibrotactile letter recognition

Research with the Tactile Vision Substitution System, a device that converts optical patterns into vibrotactile patterns for display against the back, has shown that a simple pattern, such as a letter, is more easily recognized when presented sequentially than when presented in entirety all at once. In recent work with the Optacon, another such device using the surface of the finger for display, Craig (Note 2) has found quite the opposite result over an extensive range of pattern durations. The present study shows that the superiority of sequential presentation can be obtained with the Optacon if letters considerably smaller than usual are displayed. Sequential presentation is advantageous when the pattern information essential for recognition exceeds the spatial bandwidth of the sensory surface, whether it be the finger, back, or other skin surface. In the normal usage of the Optacon, however, it appears that the spatial bandwidth of the finger suffices for the recognition of large roman letters.

Modes of vibrotactile pattern generation.

Two modes of generating vibrotactile patterns, static and scanned, were examined. In the static mode, all elements making up the pattern were turned on and off simultaneously. In the scanned mode, the pattern to be identified was moved across the tactile array. The patterns were letters of the alphabet presented to the fingertips by means of the Optacon, a reading aid for the blind. The results of the first experiment showed that the performance on a letter recognition task decreased as pattern duration decreased and that at all durations below 200-msec performance in the static mode was better than in the scanned mode. Good letter recognition was possible at durations of 4 msec in the static mode. The results of the second experiment showed that letter recognition in the static mode was highly dependent on the perceived intensity of the letters presented, whereas intensity changes in the scanned mode had little effect on letter recognition. The results of the third experiment showed that both modes of pattern presentation produced similar results in the presence of masking stimuli. The implications of the results for cutaneous pattern perception and information transmission and visual letter recognition are discussed.

Effects of vibrotactile feedback upon the production of co‐articulated CV syllables

Eight profoundly deaf and deaf/blind children are receiving ongoing training in the production of speech sounds. An electrocutaneous sensory aid, worn around the abdomen, displays the speech sounds of the teacher and the child as vibrotactile patterns. In the first training activity, the syllables /ba (ba)/, /bee (bi)/ and /boo (bu)/ were presented (1) as a 2‐s sustained utterance (to assess the child's ability to control articulators in sustaining a vowel), and (2) as a three‐syllable utterance, repeated at a 3/s rate (approximating the rate of normal speech). Training stimuli were presented by videotape, and the children's responses were recorded and spectro‐graphically analyzed, over a training period of three weeks. An analysis was made of the suprasegmental features of pitch and rhythm, as well as the articulatory features of transition and formant structure. The children's performance was compared under two conditions, one while wearing their hearing aids plus the vibrotactile belt, the other with hearing aids alone. [Work supported by NIH.]

The discrimination of vibratory patterns on a tactile matrix

The ability of observers to discriminate static vibrotactile patterns was examined on a tactile matrix of 64 vibrators. Observers were presented with pairs of patterns that varied in symmetry, number of pattern elements (numerosity), and number of common pattern elements (communality), and were asked to judge whether the members of the pair were the same or different. Errors were primarily related to communality, while variation in symmetry had no effect on performance. Only at high levels of communality did numerosity affect performance differentially. Confusions resulted when few of many elements in the patterns differed. The levels of performance were found to be inferior to those reported by investigators who examined such relationships in patterns presented to more widespread body loci. A discussion of models of confusion in such tasks is presented.

Identification of speech sounds displayed on a vibrotactile vocoder.

A vocoder-type speech analyzer interfaced to the tactile display of an Optacon was used to investigate how subjects learned, over a six-week period, to identify the vibrotactile patterns of different speech signals. Closed sets of four vowel durations, three different vowels, and four spondee words constituted the test material. Learning to identify vibrotactile patterns required many hours of training. Subjects in this study showed significant improvement in the identification of all three types of speech signals, especially the vowel durations and spondee words. Tests for transfer at the end of training showed that shifting the locus of stimulation did not result in decrement in performance.

Vibrotactile Pattern Perception: Extraordinary Observers

Two sighted peopled showed a remarkable ability to perceive vibrotactile patterns generated by the Optacon, a reading aid for the blind. These individuals were able to read at very high rates, 70 to 100 words per minute, through their fingertips. Additional testing showed them to be much better than other people at discriminating and recognizing vibrotactile patterns.

Temporal Ordering of Events in Haptic Space

The most rapid acquisition of skill in the use of complex vibrotactile displays will occur when the capabilities of the organism are most efficiently exploited by the display code. When spatiotemporal patterns are chosen as the coding scheme, the problem of perception of temporal order is of great importance. The present paper describes the effects on the limen for order of two events, of the quality of the stimuli, their spacing on the body, and their intensive relations. The results suggest the presence of limiting conditions for the spatial and, by analogy, the temporal density of vibrotactile patterns. Comparisons are made with results reported previously, and a hypothesis is developed concerning the onset and timing of stimuli in relation to the capacity of the nervous system to augment the clarity of sensory events and to transfer the argumentation to successive locations on the sensory surface.