885095962

ms were delivcred at 25-100 Hz in a row-by-row scquencc stimulating motion of a horizontal bar along the finger. These stimuli activated only phasic mcchanorcceplors (RA and PC afferents) but not slowly adapt-ing afferents. RA afferents view only a smali fraction of spatial pattems, as they respond to only 2-4 adjacent rows, firing one spike/pulsc. Responses arc all or nonę, and constant throughout thc 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 mimie the stimulation frequency. Central neural networks transform the peripheral input such that S-l 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 ratę at 25 Hz, and reduced to half the input frequency at 100 Hz, suggesting amplification at Iow Hertz and inhibition at high Hertz. Stimulation rates are represented by the pattem of firing within the spike train, but the modulation amplitudę is frequency dependent. It is suggested that the low-amplitude contin-uous firing observed at 100 Hz correlates with sensations of smooth motion across the finger. while the large fiuctuations in neural excitability at 25 Hz yield distinct, punctate sensations. [Work supported by NS11862.]

3:50-4:00

Break

Contributed Papers

4:00

9BV7. Identifying the direction of simulated movement on the skin: The eflfects of an irrelevant stimulus. Paul M. Evans (Dept. of Psychol., 900 State St., Willamette Univ., Salem, OR 97301) and James C. Craig (Indiana Univ., Bloomington, IN 47405)

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 lefl 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 rcmaining stimuli. The subjecfs 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 thc same response; and (3) thc stimuli were difTerent 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 rcaction limes were faster than when the nontarget and target had different responses. The results suggest that subjects are unable to restriet proccssing to a single site on thc hand. Moreover, a tactile stimulus at a nontarget location appears to be pro-cessed to the level of response activation. (Work supported by NIH.]

4:15

9BV8. Judgments of tactile texture gradient magnitude. Gunnar Jansson (Dept. of Psychol., Uppsala Univ., Box 1854, S-751 48 Uppsala, Sweden) and Barry Hughes (Univ. of Illinois at Chicago, Chicago, IL 60680)

A main problem in reading tactile pictures is the perception of depth. In visual pictures, texture gradients are very effective in provid-ing 3-D information. The aim of this study was to investigate one aspect of this potential source of information in tactile pictures, namely, judg-ment of the magnitude of tactually presented texture gradients. The stimuli consisted of polar projections of regular piane pattems of points and lines at a slant from the frontal piane. Such projections were copied onto swell paper which, after heating, provided the texture gradient in imbossed form. The pattems were read with the tip of the index finger without any restrictions conceming 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 expcri-ments, investigating hypotheses derived from analyses of recordings of the exploratory movcments, with stimuli containing either the whole gradient, its central part, or its extremes demonstrated very similar results for the whole gradient and its extremcs. The theoretical signifi-cance of these results is discussed.

4:30

9BV9. Vibrotactile thresholds for detectlon of sinusoidal vibration as a function of stimulus duration measured in the presence of vibratory background noise. G. A. Gescheider (Hamilton College, Psychol. Dept., Clinton, NY 13323 and Syracuse Univ., Inst. for Sensory Res., Merrill Lane, Syracuse, NY 13210-5290), Kathleen Hoffman, Michael Travis (Hamilton College, Clinton, NY 13312), Stanley J. Bolanowski, Jr., and Ronald T. Verrillo (Syracuse Univ., Syracuse, NY 13210-5290)

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 inereases, 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 smali 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 predictablc from the hypothesis that temporal summation can occur in the Pacinian, but not in one of the non-Pacinian channels.

2004 J. Acoust. Soc. Am., Vol. 89, No. 4, Pt. 2, April 1991

121st Meeting: Acoustical Society of America 2004