The effects of variations in stimulus duration and interstimulus onset interval on ratings of tactile apparent movement were determined for seven Ss with stimulators of very small diameter. Judgments of successiveness and simultaneity were also obtained. It was found that apparent movement increased as a power function of increases in stimulus duration. The function relating tactile apparent movement and stimulus duration was shown to be similar to that obtained by Kolers (1964) for visual apparent movement. Interstimulus onset interval also had a marked effect on apparent movement, and the optimal interval was influenced by stimulus duration in a manner similar to that reported by Sherrick and Rogers (1966). This study was originally motivated by observations made in the course of research on a tactile display for speech. Since one aim of that research was to present spatiotemporal tactile patterns that could be perceptually integrated over time, an attempt was made to produce good apparent movement between successive stimuli. The need for spatiotemporal integration in tactile displays of speech and language and the relevance of apparent movement for such perceptual integration has been discussed elsewhere (Kirman, 1973).. Sherrick and Rogers (1966) had observed good apparent movement with very brief tactile stimuli similar to those employed in this research. Accordingly, an interstimulus onset interval (ISOI) was chosen which was very close to that reported by these researchers to produce optimal tactile apparent movement with such stimuli. Although some features of the tactile stimuli were different from those utilized by Sherrick and Rogers, it was not expected that the temporal conditions for good apparent movement would be affected. These authors had reported that virtually. identical temporal intervals produced optimal apparent movement regardless of whether the stimuli werevibrotactile, electrocutaneous, or even visual. The observations with the tactile display were, however, disappointing. Instead of good apparent movement, Ss reported separated stimuli following each other in clear succession.Neither the work of Sherrick and Rogers nor other studies of tactile apparent movement indicated any basis for the discrepancy in results. The few investigators that had successfully obtained tactile apparent movement were not in complete agreement on which stimulus variables are of major significance for the phenomenon. While Sumby (1955) had found ISOI to be important and had determined the optimal interval for one stimulus duration, Gibson (1963) reported that ISOI was not a variable of any consequence over a wide range of stimulus durations, including the duration studied by Sumby. Sherrick and Rogers (1966), investigating the *This research was supported by Public Health Service Grant 2 ROI NS 06205. same range of stimulus durations, observed Ism to be a major variable for all durations, in contrast to Gibson's findings. Gibson (1963) also reported that the impressiveness of tactile apparent movement was ...

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The effect of variations in the number of sequentially activated electromechanical stimulators on tactile apparent movement was examined in nine subjects. Judgments of successiveness or simultaneity were obtained as well. It was observed that four stimulators produced more frequent reports of apparent movement and resulted in optimal movement at shorter interstimulus onset intervals than did two stimulators. regardless of stimulus duration. Stimulus duration and interstimulus onset interval and their interaction were again found to be important determinants of tactile apparent movement.In a recent article (Kinnan. 1973>. it was suggested that rapidly comprehensible tactile displays of speech or language should permit the perceptual integration of successively presented stimuli into relatively large linguistic units. It was also proposed that. if the proper spatial and temporal conditions were provided. the illusion of tactile apparent movement could serve as a mechanism for the integration of such stimuli into unitary percepts. However. requirements for the emergence of tactile apparent movement have not been determined for a sufficiently wide variety of stimulus conditions to provide practical guidelines for the designer of such tactile displays.Most investigations of the phenomenon of tactile apparent movement have utilized two stimulators. whether vibratory or electrocutaneous. It has been established that the impressiveness ofthe illusion with two stimulators is intluenced both by stimulus duration and by the interval between their onsets. 'It has further been shown that there is a considerable interaction between these two variables (Kirman, 1974a; Sherrick & Rogers. 19(6). However. since practical punctiform tactile displays will certainly utilize more than two successive stimuli. information is needed about the effects of increasing the number of sequential stimuli.While it has been shown that increasing the number of successive stimuli enhances the impressiveness of the illusion of movement (Kirrnan, 1974b). the effect of such increases on the optimal temporal conditions for obtaining good movement has not been determined. The present experiment was designed to provide such information. METHOD SubjectsThe subjects were 9 undergraduates at Queens College of CUNY. none of whom had had any prior experience with experiments using tactile stimulation or apparent movement. They were selected from an original group of II subjects. 2 of whom were eliminated from the experiment because of the unreliability of theirjudgments. All subjects were paid by the hour for their services. ApparatusThe tactile stimulators that contacted the subjects' fingers were bronze rods ..025 in. (.04 mm) in diarn and rounded at the tip. that pushed up from I 8-in. 13.2-mm) holes in a Plexiglas rest plate which served both to maintain the finger surface in a constant position relative to the stimulators and to minimize traveling waves on the skin surface between stimulus sites. These rods were direct extensions of the spring-loaded ar...

Judgments of tactile apparent movement were obtained from six subjects for a variety of tactile spatiotemporal stimulus patterns (moving points and lines, rotating lines, and expanding squares, boundaries, and holes). Each of these patterns was presented by means of three different numbers of steps used to trace the pattern over time. Stimulus duration and interstimulus onset interval (lSOI) were varied to determine the temporal conditions required for good tactile apparent movement. In general, pattern shape and type of movement (linear, rotating, expanding) had little effect on the temporal conditions for good apparent movement or on the interactions among the other variables. Increasing the number of steps in a pattern decreased the ISOI required for good apparent movement, but had no effect on the range of ISOls over which good movement was obtained. Increases in stimulus duration increased the ISOI required for good tactile apparent movement, in agreement with earlier studies, and increased as well the range of ISOls over which good movement was obtained.This experiment was stimulated by both theoret· ical and practical concerns. The theoretical interest was to examine the effects of shape and type of movement on the temporal conditions for the phenomenon of apparent movement in the tactual modality, as has been done in vision (Anstis, 1970(Anstis, , 1978Kolers, 1972). The practical concern was to proVide designers of tactile displays with an understanding of the proper spatiotemporal conditions for the emergence of good apparent movement under conditions involving tactile patterns of varying complexity, such as might result from a tactile display of speech. In particular, as I have discussed in an earlier paper (Kirman, 1973), it may be of considerable importance for a tactile display of speech to maintain a sense of continuity for some portions of the tactile stimulus stream (e.g., over syl· labic units) while providing segmenting intervals that result in clear perceptual segregation at other times. It is obviously relevant to know whether the required temporal conditions for the illusion of continuous movement vary significantly with the geometry of the shapes presented or the type of motion described.Previous experiments on tactile apparent movement have focused on only two point-stimulators or several such point-stimulators in a linear arrangement (Kirman, 1974a(Kirman, , 1974b(Kirman, , 1975Sherrick & Rogers, 1966). Whether more complex pattern shapes or directions of movement would be integratable by apparent movement at the same or similar temporal intervals was not clear. The present experiment, therefore, while including linear movement similar to that previously studied, also utilized several other shapes and types 96of motion. An additional aspect of tactile display presentation investigated here was the number of successive steps involved in presenting any given spatiotemporal pattern. For example, in presenting the trajectory of a tactile stimulus over some distance from locus A to locus B, ...

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