A Tactile Automated Passive-Finger Stimulator (TAPS)

2013

Front. Hum. Neurosci.

Self Cite

129

Two-point discrimination is widely used to measure tactile spatial acuity. The validity of the two-point threshold as a spatial acuity measure rests on the assumption that two points can be distinguished from one only when the two points are sufficiently separated to evoke spatially distinguishable foci of neural activity. However, some previous research has challenged this view, suggesting instead that two-point task performance benefits from an unintended non-spatial cue, allowing spuriously good performance at small tip separations. We compared the traditional two-point task to an equally convenient alternative task in which participants attempt to discern the orientation (vertical or horizontal) of two points of contact. We used precision digital readout calipers to administer two-interval forced-choice versions of both tasks to 24 neurologically healthy adults, on the fingertip, finger base, palm, and forearm. We used Bayesian adaptive testing to estimate the participants’ psychometric functions on the two tasks. Traditional two-point performance remained significantly above chance levels even at zero point separation. In contrast, two-point orientation discrimination approached chance as point separation approached zero, as expected for a valid measure of tactile spatial acuity. Traditional two-point performance was so inflated at small point separations that 75%-correct thresholds could be determined on all tested sites for fewer than half of participants. The 95%-correct thresholds on the two tasks were similar, and correlated with receptive field spacing. In keeping with previous critiques, we conclude that the traditional two-point task provides an unintended non-spatial cue, resulting in spuriously good performance at small spatial separations. Unlike two-point discrimination, two-point orientation discrimination rigorously measures tactile spatial acuity. We recommend the use of two-point orientation discrimination for neurological assessment.

Section: Discussionmentioning

confidence: 99%

Two-Point Orientation Discrimination Versus the Traditional Two-Point Test for Tactile Spatial Acuity Assessment

Tong¹,

Mao²,

2013

Front. Hum. Neurosci.

Self Cite

129

“…We used the tactile automated passive-finger stimulator (TAPS), described in detail in Goldreich et al (2009). Briefly, the participant's arm rested comfortably in prone position on a tabletop.…”

Section: Methodsmentioning

confidence: 99%

“…This method calculates a posterior probability density function (PDF) for each participant's threshold stimulus level, corresponding to 76% correct response probability (dЈ ϭ 1 on the 2-IFC task). We implemented the ⌿ algorithm as explained in detail in Goldreich et al (2009). Briefly, following Kontsevich and Tyler (1999), we modeled dЈ as a power function of groove width, x, and we modeled the psychometric function (the probability of correct response at x), ⌿ a,b,␦ (x), as a mixture of a cumulative normal function and a lapse rate term:…”

Section: Methodsmentioning

confidence: 99%

Tactile Spatial Acuity Enhancement in Blindness: Evidence for Experience-Dependent Mechanisms

Wong¹,

Gnanakumaran²,

2011

J. Neurosci.

151

120

Tactile spatial acuity is enhanced in blindness, according to several studies, but the cause of this enhancement has been controversial. Two competing hypotheses are the tactile experience hypothesis (reliance on the sense of touch drives tactile-acuity enhancement) and the visual deprivation hypothesis (the absence of vision itself drives tactile-acuity enhancement). Here, we performed experiments to distinguish between these two hypotheses. We used force-controlled grating orientation tasks to compare the passive (finger stationary) tactile spatial acuity of 28 profoundly blind and 55 normally sighted humans on the index, middle, and ring fingers of each hand, and on the lips. The tactile experience hypothesis predicted that blind participants would outperform the sighted on the fingers, and that Braille reading would correlate with tactile acuity. The visual deprivation hypothesis predicted that blind participants would outperform the sighted on fingers and lips. Consistent with the tactile experience hypothesis, the blind significantly outperformed the sighted on all fingers, but not on the lips. Additionally, among blind participants, proficient Braille readers on their preferred reading index finger outperformed nonreaders. Finally, proficient Braille readers performed better with their preferred reading index finger than with the opposite index finger, and their acuity on the preferred reading finger correlated with their weekly reading time. These results clearly implicate reliance on the sense of touch as the trigger for tactile spatial acuity enhancement in the blind, and suggest the action of underlying experience-dependent neural mechanisms such as somatosensory and/or cross-modal cortical plasticity.

“…The GOT has several advantages over the two-point (calipers) test as a measure of spatial acuity (Johnson and Phillips, 1981;Craig and Johnson, 2000). The testing apparatus and procedure are described in detail in Goldreich et al (2009). Briefly, grooved surfaces (20 squarewave gratings with groove widths ranging from 0.25 to 3.10 mm, in 0.15 mm increments) rose under computer control to contact the distal pad of the dominant index finger (4 cm/s onset velocity, 1 s duration, 50 g force).…”

Section: Methodsmentioning

confidence: 99%

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

Peters¹,

Hackeman²,

2009

J. Neurosci.

178

149

We have observed that passive tactile spatial acuity, the ability to resolve the spatial structure of surfaces pressed upon the skin, differs subtly but consistently between the sexes, with women able to perceive finer surface detail than men. Eschewing complex central explanations, we hypothesized that this sex difference in somatosensory perception might result from simple physical differences between the fingers of women and men. To investigate, we tested 50 women and 50 men on a tactile grating orientation task and measured the surface area of the participants' index fingertips. In subsets of participants, we additionally measured finger skin compliance and optically imaged the fingerprint microstructure to count sweat pores. We show here that tactile perception improves with decreasing finger size, and that this correlation fully explains the better perception of women, who on average have smaller fingers than men. Indeed, when sex and finger size are both considered in statistical analyses, only finger size predicts tactile acuity. Thus, a man and a woman with fingers of equal size will, on average, enjoy equal tactile acuity. We further show that sweat pores, and presumably the Merkel receptors beneath them, are packed more densely in smaller fingers.