Perceived magnitude of multiple electrocutaneous pulses.

Abstract

The subjective magnitude of electrical stimulation has been studied extensively. Usually, the function relating the electrical stimulus (current) to magnitude estimates can be approximated by a straight line on loglog coordinates, with a slope between 1.8 (Ekman, Frankenhaeuser, Levander, & Mellis, 1964, 1966; Sternbach & Tursky, 1964)and 3.5 (e.g., S. S. Stevens, Carton, & Shickrnan, 1958). The dynamic range of current that elicits sensations between threshold and pain varies inversely with this slope: high slopes correspond to small ranges (6 to 8 dB) and low slopes correspond to larger dynamic ranges (up to 20 dB). This inverse relation has been observed across many sensory modalities (e.g., Poulton, 1968; Rosenblith, 1959; Teghtsoonian, 1971, 1973), although there is disagreement over whether the relation is due to arbitrary choices of stimulus range or to true variations in stimulus dynamic range which produce the same range of sensation. This study was motivated by the view that the configuration of stimulus (e.g., the type of current waveform) might influence growth of perceived magnitude. Sinusoidal and single-pulse waveforms have been employed in other magnitude studies and have been shown to produce pain with a small dynamic range. Gibson (1968) and Saunders (1974) developed a stimulus configuration for painless electrical stimulation using multiple pulses of current. This stimulus is quantal. The Saunders scheme consists of bursts of alternating positive and negative pulses, each with a duration, T, of about to usee and a peak amplitude, Ipeak' of 10 rnA (cf. Figure 1). Average intensity is changed by increasing or decreasing the number of such pulses within each burst. We hoped such stimulations would result in shallow loudness slopes and wide dynamic range in order to facilitate coding auditory information in the intensity dimension with a cutaneous stimulator. In the present study, we have employed the method of cross-modality matching (CMM) to compare the perceived magnitude of electrical stimulation on the abdomen to that of a 500-Hz tone presented by earphones. In this way, we could compare growth of sensation magnitude for the two modalities, since our ultimate goal is to substitute the skin for the ear as a communication channe!. We could also infer the