Relative roles of spatial and intensive cues in the discrimination of spatial tactile stimuli

Abstract

Two psychophysical measures of tactile sensitivity-grating-orientation (GO) and smooth-grooved (SG) discrimination-were used to determine tactile spatial acuity with and without an intermediate surface (latex glove) interposed between the contactor and the skin. Measures were made at three locations that varied in sensitivity and in density of innervation of the primary afferent fibers: the index fingerpad (fingertip), palmar surface of the proximal phalanx (fingerbase), and the thenar eminence (palm). Neurophysiological studies have suggested that the density of innervation of SAI fibers is a limiting factor in spatial acuity. In the present study, without a glove, the GO thresholds varied as a function of location. With the glove, increases in the GO thresholds were relatively uniform and modest. Without a glove, however, the SG thresholds were well below the GO thresholds, and changing the site of stimulation had little effect on the threshold. With a glove, the SG thresholds increased by 100% to more than 300% as in comparison with those in the no-glove condition. The largest increases occurred at the less sensitive locations. The results of the GO task are consistent with the view that GO is a valid measure of spatial acuity. The results of the SG task, however, are inconsistent with previous results and suggest that both spatial and intensive factors are involved in this task.

Diminutive Digits Discern Delicate Details: Fingertip Size and the Sex Difference in Tactile Spatial Acuity

“…The precision of this neural image depends crucially on SA1 innervation density and receptive field size. The fingertip, for instance, has greater SA1 density (Johansson and Vallbo, 1979), smaller SA1 receptive fields (Schady and Torebjörk, 1983), and correspondingly better spatial acuity than does the finger base (Gibson and Craig, 2002). Anatomical (Güçlü et al, 2008) and physiological (Johansson, 1978) evidence suggests that SA1s branch to innervate several clusters of Merkel cells (Fig.…”

Tactile spatial sensitivity and anisotropy

“…For example, if subjects are clearly able to detect the presence of a grating in one orientation but not the other, then they may base their responses on detecting the presence or absence of the grating. Such a discrimination is more likely to be done on the basis of intensive rather than spatial cues (Gibson & Craig, 2002). The problem of anisotropy and spatial sensitivity is one of the focuses of the present study.…”

“…From the time of its early use, however, researchers have recognized the inherent problems with the two-point threshold as a measure of tactile spatial acuity (Boring, 1942;Friedline, 1918;Tawney, 1895;Weber, 1834Weber, /1996; for reviews, see Craig & Johnson, 2000;Johnson, Van Boven, & Hsiao, 1994; see also Van Boven & Johnson, 1994b). More recently, there have been efforts by several researchers to develop new psychophysical measures of tactile spatial acuity (Craig, 1999;Craig & Kisner, 1998;Gibson & Craig, 2002;Stevens & Choo, 1996;Stevens & Patterson, 1995).…”

“…Return to normal performance on the GR/OR task closely paralleled the rate of reinnervation of the primary afferent fibers, as well as the subject's self-report of normal sensory function (Van Boven & Johnson, 1994b). The GR/OR task has also been used as a measure of spatial acuity at a number of different locations on the skin that are known to vary in their density of innervation (Craig, 1999;Craig & Kisner, 1998;Essock, Krebs, & Prather, 1997;Gibson & Craig, 2002;Patel, Essick, & Kelly, 1997;Sathian & Zangaladze, 1996;Van Boven & Johnson, 1994a). In each case, performance on the GR/OR task roughly correlated with changes in density of innervation of the primary afferent fibers.…”

“…Performance is measured as a function of the groove width of the grating. It has been shown that performance on the GR/OR task is correlated with the density of innervation of the primary afferent fibers (Gibson & Craig, 2002;Van Boven & Johnson, 1994a, 1994b. In one study that used the GR/OR task, subjects were tested before and after oral surgery that had produced nerve damage.…”