Sensation magnitude of vibrotactile stimuli

A systematic investigation of the subjective magnitude of vibrotaction was undertaken to: (1) determine the growth of sensation as a function of stimulus intensity; (2) establish contours of equal subjective magnitude; and (3) compare over a wide range of frequency and intensity the psychophysical methods of direct scaling and intensity matching. The results show that the data obtained by direct scaling are comparable to the data obtained by interfrequency matching. The subjective magnitude function is a power function with a slope of about 0.89 for frequencies up to 350 Hz. Near threshold the growth of sensation is proportional to the physical intensity. Contours of equal subjective magnitude for vibration across 10 frequencies and at 11 levels of intensity are given.     

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.     

Equal-onset contours of vibrotactile stimuli

Characteristic sensations of “surge” occur at onset of vibratory stimulation, analogous to the experience of musical “attack” in the auditory modality. Such a cutaneous sensation may have a phenomenal reality that is discriminable from the sensitivity to either of its physical determinants of time and intensity. Contours of equal-onset sensation obtained by the method of adjustment permitted the assessment of the relative contributions of these two parameters. Both rise time and intensity were found to be significant factors in the determination of contours of equal-onset sensation obtained by either time adjustment or adjustment of vibratory intensity. Equating onset by intensity adjustment was found to be more difficult than equating onset by time adjustment.     

Spatially-limited attention to vibrotactile stimulation

Weak vibrotactile signals were presented to human Os, in some instances to the index finger alone, in other instances to the middle finger alone, and in still other instances to the two fingers simultaneously. When the 0 knew in advance of a trial which finger(s) would be presented a signal, no spatial summation resulted, that is, the sensitivity of two fingers to two signals was no greater than the sensitivity of one finger to one signal. When the 0 was left uncertain about which finger(s) would be presented a signal on any given trial, a result having the appearance of spatial summation was obtained. Theappearance is misleading;the difference between two-finger and one-finger sensitivity in this case reflects, instead, a decrement in the performance of the single fingers. Both results are consistent with a single-channel model of attention.     

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.     

Dimensional interactions in vibrotactile information processing

The effect of irrelevant dimensional variation on the processing of vibrotactile stimuli was measured. Six observers performed a speeded classification task with stimuli varying along the dimensions of pitch and loudness. Choice reaction times were obtained for stimuli differing on one dimension alone, on two correlated dimensions, or on two orthogonally varied dimensions. Compared to one-dimension performance, reaction times were faster in the correlated condition and slower in the orthogonal condition. In general, these findings agreed with similar experiments in other modalities, with the exception that the effects in this study tended to be stronger for cases in which loudness, rather than pitch, was the relevant dimension. The results are explained in terms of the integrality of pitch and loudness and of the relative discriminability of dimensions.     

Temporal integration and vibrotactile backward masking

Subjects were presented with vibrotactile target patterns to their left index fingertips. The target patterns varied in the number of line segments that they contained and were presented in the presence or absence of a backward-masking stimulus. The stimulus onset asynchrony (SOA) between the target and masker was varied. In an identification task, subjects' errors indicated that the effect of the masker at brief SOAs was to increase the perceived number of line segments in the target. This effect diminished with increasing SOA, and at the longest SOAs subjects confused targets with patterns containing the same number of line segments but varying in how the line segments were related. In an estimation task, the effect of the masker was to increase the number of line segments estimated to be contained in the target pattern. The effect of the masker at brief SOAs is discussed in terms of an integration theory of vibrotactile backward masking. At longer SOAs, the results suggest that the masker may interfere with the extraction of relational information in the target pattern.     

Contralateral enhancement and suppression of vibrotactile sensation

A psychophysical matching procedure was used to measure the effect of a conditioning stimulus on the vibrotactile sensation magnitude of a test stimulus. When both stimuli were applied to the thenar eminence of the same hand, the conditioning stimulus enhanced the sensation magnitude of the test stimulus. Enhancement was also observed when the test stimulus was on the thenar eminence and the conditioning stimulus was either on the contralateral thenar eminence, the ipsilateral middle finger, or the contralateral middle finger. When the conditioning and test stimuli were applied to separate sites, enhancement was maximal when At between the stimuli was 150 msec. At Ate less than 100 msec, suppression was observed. Enhancement and suppression were observed only when the frequencies of the two stimuli were within the same vibrotactile information processing channel.     

A behavioral study of distraction by vibrotactile novelty

Past research has demonstrated that the occurrence of unexpected task-irrelevant changes in the auditory or visual sensory channels captured attention in an obligatory fashion, hindering behavioral performance in ongoing auditory or visual categorization tasks and generating orientation and re-orientation electrophysiological responses. We report the first experiment extending the behavioral study of cross-modal distraction to tactile novelty. Using a vibrotactile-visual cross-modal oddball task and a bespoke hand-arm vibration device, we found that participants were significantly slower at categorizing the parity of visually presented digits following a rare and unexpected change in vibrotactile stimulation (novelty distraction), and that this effect extended to the subsequent trial (postnovelty distraction). These results are in line with past research on auditory and visual novelty and fit the proposition of common and amodal cognitive mechanisms for the involuntary detection of change.     

Effects of the menstrual cycle on vibrotactile sensitivity

Psychophysical thresholds for the detection of vibration delivered to the thenar eminence of the right hands of young males and females were measured every other day for 30–34 days. The frequency of the vibratory stimulus was either 15 or 250 Hz. The sinusoidal stimuli applied through a 3.0-cm² contactor were 700 msec in duration and had rise-fall times of 25 msec. Stimulus amplitude was measured with a calibrated accelerometer mounted on the moving element of the vibrator. Data were plotted as a function of successive days in the menstrual cycle. Thresholds for detecting the 15-Hz stimulus did not change significantly, whereas thresholds for detecting the 250-Hz stimulus varied significantly over the menstrual cycle. The 250-Hz threshold became progressively lower as subjects approached the onset of menstruation. After the onset of menstruation, the 250-Hz threshold gradually increased, reaching a maximum value approximately 12 or 13 days later. Soon after the 12th or 13th day of the cycle, the threshold again began to decline and continued to decline until the onset of the next menstrual cycle. The thresholds of women taking birth control pills did not change systematically over the testing period.     

User perceptions and evaluations of short vibrotactile feedback

The objective of the present study was to provide a better understanding of the factors that influence discrimination and subjective assessment of vibrotactile feedbacks during active interaction with a touchscreen. Twenty-four participants were presented with 162 pairs of vibrotactile signals that varied in frequency (60 Hz, 130 Hz, 200 Hz), waveform (sine, square and triangle), and duration (around 123 ms for short and 163 ms for long). Participants had to complete three successive tasks: a dissimilarity task, a preference judgement task, and a resemblance (to push-buttons) judgement task. For the discrimination task, a MultiDimensional Scale analysis revealed: (1) a predominant role of frequency, (2) a role of duration for a given frequency, and (3) no role of waveform. An analysis of variance performed on the preference and resemblance data also point out the main role of the signal frequency. Finally, a correlation was found between preference and resemblance data, indicating that the participants tend to prefer signals judged to be similar to familiar tactile sensations.     

Temporal summation effects on lingual vibrotactile thresholds.

Ascending lingual vibrotactile thresholds at 250 Hz were obtained for four groups of normal-speaking adult subjects. Stimulus durations were varied for each respective group. Threshold values plotted as a function of stimulus duration indicated a temporal summation function occurring up to 200 msec. Findings are discussed in terms of underlying peripheral receptors and some implications for using summation measures as a basis for identifying oral sensory disorders.