Vibrotactile adaptation enhances amplitude discrimination

Abstract

Human psychophysical detection and amplitude discrimination thresholds for 25-Hz sinusoidal vibrations were measured on the thenar eminence using two-interval forced-choice tracking, in the unadapted state and following exposure to 25-Hz adapting stimuli representing a range of amplitudes (5-25 dB SL). As expected, detection threshold was elevated 6 to 7 dB for each 10-dB increase in the adapting stimulus. In contrast, amplitude difference thresholds for 10 and 20 dB SL standard stimuli were generally lowest when the amplitude of the adapting stimulus was equal to the amplitude of the standard. The results indicate that while adaptation impairs detection of a liminal vibrotactile stimulus, it improves intensity discrimination of supraliminal stimuli that are close in amplitude to the adapting stimulus. The compatability between these results and a recently proposed model of cortical dynamics (Whitsel et al., 1989) suggests that cortical events may contribute significantly to the physiological basis of vibrotactile adaptation.

Effects of adaptation on the capacity to differentiate simultaneously delivered dual-site vibrotactile stimuli

“…The effects of delivering an adapting stimulus on the perception of subsequent test stimuliparticularly the reduction in sensation -has been characterized in some detail (Delemos and Hollins, 1996;Gescheider et al, 1995;Goble and Hollins, 1993;Laskin and Spencer, 1979;Tommerdahl et al, 2005a;Verrillo and Gescheider, 1977). Many psychophysical studies have reported that the presentation of an adapting stimulus causes an increase in the detection threshold, and thus a reduction in the perceived intensity, of a subsequent stimulus (for review see (Gescheider et al, 1995;Goble and Hollins, 1993;Verrillo, 1985;Verrillo and Gescheider, 1977)).…”

“…Many psychophysical studies have reported that the presentation of an adapting stimulus causes an increase in the detection threshold, and thus a reduction in the perceived intensity, of a subsequent stimulus (for review see (Gescheider et al, 1995;Goble and Hollins, 1993;Verrillo, 1985;Verrillo and Gescheider, 1977)). More specifically, Gescheider et al showed that the threshold shift which occurred after the presentation of an adapting stimulus increased systematically with adapting stimulus duration (Gescheider et al, 1995).…”

“…Fewer studies, however, have examined the impact of an adapting stimulus on the perceptual task of amplitude discrimination. Goble and Hollins reported that while an adapting stimulus increased the threshold for detection of a subsequent stimulus, it also enhanced a subject's ability to discriminate subtle differences in the intensity of two subsequent (suprathreshold) stimuli which were presented serially to the same site (Goble and Hollins, 1993). One important difference of note between the protocol implemented in this study versus that in the Goble and Hollins study, in addition to simultaneously delivered stimuli, is that the duration of adaptation in that study was much longer (15 sec adapter followed by two 1 sec test stimuli).…”

A portable tactile sensory diagnostic device

“…Two point discrimination (Vierck and Jones, 1970;Tannan et al, 2005a;Tannan et al, 2005b), measures of spatial acuity (Tannan et al, 2006;Tommerdahl et al, 2007), frequency discrimination (LaMotte and Mountcastle, 1975), temporal order judgment (Fiorio et al, 2003), and changes in responsivity with adaptation (Goble and Hollins, 1993;Tommerdahl et al, 2005c) are all examples of methods which could be easily implemented and/or modified with this device and could prove useful as sensory diagnostics in a number of clinical and/or clinical research settings. A number of features of this tactile stimulator system make it unique from previously reported devices, and these features will have a positive impact on its potential use in such non-laboratory settings.…”

“…The delivery of sinusoidal displacements to a single skin site via mechanical transducer has been used extensively for the study of flutter vibration in both psychophysical and neurophysiological settings for a number of decades (exemplary uses of such a device are described in (Mountcastle et al, 1969;Vierck and Jones, 1970;LaMotte and Mountcastle, 1975;Juliano et al, 1989;Goble and Hollins, 1993;Tommerdahl et al, 1993;Tommerdahl et al, 1998;Tommerdahl et al, 2002)). Typically, stimuli that can be delivered through mechanical transducers -vertical displacement stimulators such as the one originally described by Chubbuck (Chubbuck, 1966) -that are used for studies of somatosensation are very well equipped to deliver sinusoidal stimuli at a frequency range (1 -250 Hz) with amplitudes of sufficient size (between 0 and 1000 μm) to activate a broad range of mechanoreceptors.…”