The Journal of Neuroscience, May 17, 2006, 26(20):5582-5588; doi:10.1523/JNEUROSCI.0028-06.2006
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Behavioral/Systems/Cognitive
Somatosensory Coding of Roughness: The Effect of Texture Adaptation in Direct and Indirect Touch
Mark Hollins,1,2
Florian Lorenz,1 and
Daniel Harper1
1Department of Psychology and 2Curriculum in Neurobiology, University of North Carolina, Chapel Hill, North Carolina 27599
Correspondence should be addressed to Dr. Mark Hollins, Department of Psychology, CB 3270, Davie Hall, University of North Carolina, Chapel Hill, NC 27599. Email: mhollins{at}email.unc.edu
To examine somatosensory mechanisms contributing to the perception of roughness, subjects examined surfaces with rigorously specified spatial textures under conditions of direct moving contact between the fingertip and the surface (direct touch) and contact through a rigid probe (indirect touch). Subjects were trained to scan the surfaces along a consistent path and with a speed of 2.7 cm/s. With each mode of touch, periods of prolonged inspection of a single adapting surface were followed by shorter periods in which the roughness of multiple test surfaces was reported. Adaptation caused a drop in perceived roughness under conditions of indirect touch, reflecting the reduced sensitivity of vibrotactile mechanisms that are the main recipients of textural information transmitted through the probe. During direct touch, adaptation had no significant effect on the perception of textures with spatial period >200 µm, which are spatially encoded. The results have an important implication for the physiological basis of the spatial code, which is believed to involve somatosensory cortical neurons with highly structured receptive fields: these cortical populations appear to be less susceptible to adaptation than otherwise similar neuronal populations in the visual system.
Key words: roughness; somatosensory coding; texture; adaptation; direct touch; indirect touch
Received May 16, 2005;
revised March 23, 2006;
accepted April 18, 2006.
Correspondence should be addressed to Dr. Mark Hollins, Department of Psychology, CB 3270, Davie Hall, University of North Carolina, Chapel Hill, NC 27599. Email: mhollins{at}email.unc.edu
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