Magnitude scales for electrocutaneous stimulation

The application of Stevens’s power law to the sensation resulting from electrocutaneous stimulation is reviewed. Its use for data from individual observers as well as pooled data from several observers is discussed. Magnitude estimates were obtained from 33 observers of the sensation resulting from electrocutaneous stimulation over the median nerve. Seven mathematical functions were applied to the data and tested for goodness of fit. The power function with or without threshold correction factor did not emerge as better than alternative functions. Difficulties in using the power function in studies of individual differences are reviewed. It is concluded that there is no adequate reason at present to discard the linear function in favor of more complex functions in psychophysical scaling of sensation induced by electric shock.     

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

Three experiments were conducted in an effort to evaluate the ability of observers to identify the direction of brief-duration spatiotemporal patterns applied to the skin. In Experiment 1, observers were required to identify the direction of linear sweeps of electrical stimulation having varying total durations (sweep durations). Performance was evaluated at several loci on the body. The effects of stimulator number and spacing on the identification of sweep direction were evaluated in Experiment 2. In Experiment 3, the effects of temporal sequencing of stimuli on the “apparent movement” phenomenon were evaluated at two body loci: the forearm and the abdomen. The results from all three experiments suggest that the ability to identify the direction of spatiotemporal sweeps can be heavily influenced by body locus, number, and spacing of electrodes. In short, the design of the tactile display may have important ramifications to the success of any sensory substitution transform hardware.     

The effect of intensity of visual stimulation upon auditory acuity

The Psychological Record -     

The effect upon monaural sensitivity of continuous stimulation of the opposite ear

The threshold to a 1,000 c./sec. tone presented to the left ear was measured whilst the right ear was under continuous stimulation by a 400 c./sec. tone. Observations were made, on different groups of subjects, under three stimulus conditions and two conditions of attention. Thresholds were found to increase with increasing intensities of the continuous tone. Attention to that part of the field associated with the continuous stimulus produced no significant change, whether the continuous stimulus was present or not. There were no significant after-effects during ten minutes following the end of the continuous stimulus, though the results suggested a slow decrease in threshold.

Several explanations of the phenomenon are considered. Cross-hearing and the reflex contraction of the middle-ear muscles can be virtually excluded. Central inhibition or the central control of sensory end-organs can account for the results. A statistical hypothesis is also tenable.     

The perceptual properties of electrocutaneous stimulation: Sensory quality,subjective intensity,and intensity-duration relation

A preliminary and two main experiments designed to examine the perceptual properties of electrocutaneous stimulation are reported. The stimuli used were single short pulses varying in intensity and duration. In Experiment 1, the exponents of power functions fitted to electrocutaneous magnitude estimation data were determined together with the sensory qualities induced by electrical stimulation. The results showed that there was no correlation between the exponent values and the sensory qualities. The mean exponent was 1.2. In Experiment 2, an intensity-duration trading function was constructed from the data obtained from identifying the induced sensory qualities. The results showed that the critical duration increases from 30 to 300 msec with increasing sensation level. These findings are compared with the properties of other sense modalities.     

Perception of two-component electrocutaneous stimuli

Electrocutaneous stimuli varying in strength (6, 8, 10 V) and frequency (9, 27, 81 Hzj were presented in pairs. Subjects were asked to give a numerical score to represent their perception of overall difference in a pair. To assess their ability to use numbers and their performance on unfamiliar stimuli, no guidance on the nature of the stimuli or the range or scale of the scores was given. Dimensional analysis indicated that perception of differences in one component was influenced by the absolute level of the other component, if this was constant in the pair, or by the difference. Considerable variation among subjects in the nature and extent of this interference effect was observed. Individual differences scaling (INDSCAL) enabled a satisfactory consensus model to be obtained. An empirical relationship expressing the observed twocomponent difference scores in terms of one-component scores was derived. Increasing voltage level diminished perception of frequency difference. Higher frequency levels augmented perception of voltage difference. This relationship is a modification of the combinatorial model proposed by Krantz and Tversky (1975). Individual differences in the combinatorial process are allowed for by application of the subject weightings from the INDSCAL solution.     

The effects of prior stimulation upon contour perception of moving stimuli

The Psychological Record -     

Partial integration of single electrocutaneous pulses

Psychometric functions generated by single eleetroeutaneous stimuli yielded a median coefficient of variation ( σ/μ ) of 0.23. These data are consistent with other psychometric data recently reported by us which yielded σ/μ ratios of this size. The data are discussed and related to conflicting data reported in the recent literature indicating coefficients of variation for this mode of stimulation which are only 1/3 as large. Evidence is presented for partial temporal summation (time-intensity reciprocity) for electrocutaneous stimuli ranging from 175 to 610 microseconds. The data are best fitted by the equation I x t^a = k, where a is approximately 0.57. This equation and exponent also fit summation data reported by the same authors who report finding steep psychometric functions. Clearly, then, the mechanism responsible for the very limited temporal summation found for eleetrocutaneous stimulation and the mechanism responsible for very steep psychometric functions are not identical. The discussion also includes speculation regarding possible mechanisms and suggestions for research.