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Apr 1991

Volume 89, Issue 4B, pp. 1851-2015

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back to top Session 9BV: Bioresponse to Vibration: Tactile Pattern Perception: Psychophysics and Neurophysiology
Invited Papers
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Expansions and modifications of the four‐channel model for touch (A)

S. J. Bolanowski

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2002-2002 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The model proposing that there are four distinct channels mediating the mechanical aspects of touch [Bolanowski et al., J. Acoust. Soc. Am. 84, 1680–1694 (1988)] was based on psychophysical and physiological experiments conducted on the glabrous skin of humans and required assumptions regarding the neural code used by each channel. Continuing psychophysical experiments have expanded the model to include hairy skin which, in the least, operates using three separate channels: a low‐frequency (0.4–3 Hz) one that is temperature insensitive, and middle‐ (3–50 Hz) and high‐ (50–500 Hz) frequency ones that are both sensitive to temperature. The sensitivity of all of these channels is greater for larger stimulus areas. Furthermore, physiological experiments directed at testing some of the assumptions used in the model to establish the psychophysical‐physiological link show that it must be modified. In particular, activity arising from a single Pacinian corpuscle cannot account for the increases in sensitivity that occur for increases in stimulus duration required by the phenomenon of temporal summation known to exist in the P channel. Therefore, it is likely that the neural code for threshold in the P channel requires the activation of more than one Pacinian corpuscle. This finding may have implications regarding the neural code used by other channels possessing temporal summation (e.g., NP II).
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Vibrotactile adaptation (A)

Mark Hollins, Alan K. Goble, and Kimberly A. Delemos

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2002-2002 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Perception of a vibratory test stimulus is substantially influenced by the level of vibrotactile stimulation that precedes it. In a series of experiments reported here, effects of such adaptation on detection and discrimination thresholds were examined. All stimuli were sinusoidal vibrations delivered perpendicular to the skin through a flat, circular contactor; thresholds were measured during “probe” test periods separated by adapting periods. Absolute thresholds showed a negatively accelerated rise following onset of the adapting stimulus, on both the hand and the face. In contrast to the fact that receptoral channels serving the hand adapt independently of one another [R. T. Verrillo and G A. Gescheider, Sens. Proc. 1, 292–300 (1977)], some evidence was found for channel interaction on the face, a result implying central nervous system (CNS) involvement. Amplitude difference thresholds, measured on the hand with two‐interval forced‐choice tracking, decreased following exposure to adapting stimuli comparable in amplitude to the test stimuli; this finding is consistent with data [G. A. Gescheider and G. H. Wright, J. Exp. Psychol. 77, 308–313 (1968)] showing that the psychophysical function is steeper after adaptation. A recently proposed model of somatosensory cortical dynamics [B. L. Whitsel et al., in Information Processing in the Somatosensory System, edited by O. Franzen and J. Westman (MacMillan, London, 1990)] offers a plausible physiological context for understanding these results. [Work supported by USPHS Grant No. DE‐07509.]
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Cortical representations of learned vibrotactile stimuli (A)

M. M. Merzenich

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2003-2003 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Recent electrophysiological studies have shown that cortical somatosensory representations are shaped by tactual experiences. These adaptive neuronal processes underlying cortical contributions to tactual learning and nondeclarative memory have been studied by: (a) distorting the factual experiences of monkeys and rats over a limited time epoch; (b) determining the consequences of special skin and peripheral nerve manipulations that test hypotheses about the neural network origins and cortical plasticity; (c) evaluating the consequences, for cortical representation and cortical network organization, of the perturbation of the network by microstimulation; and (d) training monkeys to make distinctions about tactile stimuli while tracking training‐induced changes in their cortical representations. These studies bear significance for understanding the neural origins of tactile perception, and provide a basis for understanding how idiosyncratic tactual perceptual abilities emerge from tactile experience. [Work supported by NIH Grant NS‐10414, the Coleman Fund, and Hearing Research, Inc.]
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Altering tactile spatial sensitivity (A)

James C. Craig

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2003-2003 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Recent animal studies have demonstrated that extended tactile experience can alter cortical organization [Jenkins et al., J. Neurophysiol. 63, 82–104 (1990)]. The present study examined the effect of extended tactile stimulation on spatial sensitivity in human subjects. Four subjects received repetitive, tactile stimulation presented on the volar surface of the forearm. The tactile stimuli, taps, were delivered periodically through small vibrators worn by the subjects for up to 18 h per day. After a period of 5 to 8 weeks of wearing the vibrators, three of the four subjects reported anomalous sensations when attempting to localize tactile stimuli. Subjects had difficulty in localizing stimuli and reported sensations of pressure and diffuseness. Single stimuli applied to the forearm would sometimes evoke double and triple sensations separated by as much as 20 cm. After removing the vibrators, subjects continued to report anomalous sensations for up to 15 weeks. These results suggest that the neural organization of human subjects may be altered by extended tactile experience.
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Neural mechanisms of tactual roughness perception (A)

Kenneth O. Johnson, Charles E. Connor, and Steven S. Hsiao

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2003-2003 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The neural mechanisms underlying tactual roughness were investigated in a combined psychophysical and neurophysiological study. Stimuli consisted of surfaces embossed with dot arrays of varying dot diameter and spacing. Human subjects scanned the surfaces tactually and responded with numerical magnitudes proportional to their sense of roughness magnitude. The same surfaces were scanned across the receptive fields of cutaneous mechanoreceptive afferents in monkeys while recording the evoked action potentials. Hypothetical neural codes for roughness magnitude were computed from the neural response patterns and tested for their ability to account for the psychophysical data. Four types of neural coding mechanisms were considered: (1) mean firing rate; (2) general variation in firing rate; (3) short‐term temporal variation in firing rate; and (4) local spatial variation in firing rate. Mean firing rate failed to explain the psychophysical results: Surfaces that evoked the same firing rate evoked very different roughness judgments. In contrast, neural codes based on spatial firing rate variation, especially in slowly adapting afferents, account for the psychophysical results [Connors et al., J. Neurosci. 10, 3823–3826 (1990)]. [Work supported by NIH.]
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Representation of spatial patterns on the Optacon in the peripheral and central nervous system (A)

E. P. Gardner, C. I. Palmer, H. A. Hamalainen, and S. Warren

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2003-2004 (1991); (2 pages)

Online Publication Date: 14 Aug 2005

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The pattern of neuronal activity evoked by the Optacon stimulator has been defined for cutaneous mechanoreceptors and for cortical neurons using bar patterns scanned across the tactile array. Pulses of 4 ms were delivered at 25–100 Hz in a row‐by‐row sequence stimulating motion of a horizontal bar along the finger. These stimuli activated only phasic mechanoreceptors (RA and PC afferents) but not slowly adapting afferents. RA afferents view only a small fraction of spatial patterns, as they respond to only 2–4 adjacent rows, firing one spike/pulse. Responses are all or none, and constant throughout the period of stimulation. Resolution of stripe spacing appears limited by the receptive field diameter. Total spike output is constant at all frequencies tested, and average firing rates mimic the stimulation frequency. Central neural networks transform the peripheral input such that S‐I cortical neurons show a linear rise in total spike output and constant average firing rates as the interpulse interval is lengthened from 10–40 ms. Firing is higher than the stimulation rate at 25 Hz, and reduced to half the input frequency at 100 Hz, suggesting amplification at low Hertz and inhibition at high Hertz. Stimulation rates are represented by the pattern of firing within the spike train, but the modulation amplitude is frequency dependent. It is suggested that the low‐amplitude continuous firing observed at 100 Hz correlates with sensations of smooth motion across the finger, while the large fluctuations in neural excitability at 25 Hz yield distinct, punctate sensations. [Work supported by NS11862.]
Contributed Papers
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Identifying the direction of simulated movement on the skin: The effects of an irrelevant stimulus (A)

Paul M. Evans and James C. Craig

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2004-2004 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Movement was simulated on the index and middle fingerpads by activating, in rapid succession, adjacent columns (or rows) of the tactile display of the Optacon. The stimuli either moved from left to right (or vice versa), or from the top of the display to the bottom (or vice versa). Subjects were trained to respond “1” for two of the stimuli and “2” for the remaining stimuli. The subject's task was to focus attention on the index fingerpad (the target location), to identify the stimulus that was presented to that site, and to ignore the stimulation on the middle fingerpad (the nontarget location.) There were three trial types: (1) the stimuli were physically identical (moved in the same direction; (2) the stimuli were physically different but assigned the same response; and (3) the stimuli were different and assigned different responses. The results showed that when the nontarget and target had the same response (regardless of whether they were physically identical or not), accuracy was higher and reaction times were faster than when the non‐target and target had different responses. The results suggest that subjects are unable to restrict processing to a single site on the hand. Moreover, a tactile stimulus at a nontarget location appears to be processed to the level of response activation. [Work supported by NIH.]
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Judgments of tactile texture gradient magnitude (A)

Gunnar Jansson and Barry Hughes

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2004-2004 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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A main problem in reading tactile pictures is the perception of depth. In visual pictures, texture gradients are very effective in providing 3‐D information. The aim of this study was to investigate one aspect of this potential source of information in tactile pictures, namely, judgment of the magnitude of tactually presented texture gradients. The stimuli consisted of polar projections of regular plane patterns of points and lines at a slant from the frontal plane. Such projections were copied onto swell paper which, after heating, provided the texture gradient in imbossed form. The patterns were read with the tip of the index finger without any restrictions concerning kind of exploratory movements. The result was that the tactile texture gradients were judged well in accordance with the physical magnitude of the gradient. Other experiments, investigating hypotheses derived from analyses of recordings of the exploratory movements, with stimuli containing either the whole gradient, its central part, or its extremes demonstrated very similar results for the whole gradient and its extremes. The theoretical significance of these results is discussed.
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Vibrotactile thresholds for detection of sinusoidal vibration as a function of stimulus duration measured in the presence of vibratory background noise (A)

G. A. Gescheider, Kathleen Hoffman, Michael Travis, Stanley J. Bolanowski, Jr., and Ronald T. Verrillo

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 2004-2004 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Thresholds for the detection of sinusoidal vibration were measured for stimuli ranging in duration from 15 to 1000 ms. The test stimuli were 250‐Hz bursts of vibration with 10‐ms rise‐fall times applied through either a 3.0 or 0.01 cm2 contactor to the thenar eminence of the right hand. Thresholds were measured in the presence of and in the absence of narrow‐band noise with frequencies centered around that of the test stimuli. Temporal summation, as indicated by a decrease in thresholds as stimulus duration increases, was observed at all intensities of the noise masker. This was true whether the stimulus was delivered through a large contactor designed to stimulate the Pacinian channel or through the small contactor designed to stimulate non‐Pacinian systems. On the other hand, when stimuli were detected in the presence of sinusoidal maskers, the amount of temporal summation depended on the intensity of the masker in a way predictable from the hypothesis that temporal summation can occur in the Pacinian, but not in one of the non‐Pacinian channels.
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