title: The tactile motion aftereffect suggests an intensive code for speed in neurons sensitive to both speed and direction of motion.
abstract: Neurophysiological studies in primates have found that direction-sensitive neurons in the primary somatosensory cortex (SI) generally increase their response rate with increasing speed of object motion across the skin and show little evidence of speed tuning. We employed psychophysics to determine whether human perception of motion direction could be explained by features of such neurons and whether evidence can be found for a speed-tuned process. After adaptation to motion across the skin, a subsequently presented dynamic test stimulus yields an impression of motion in the opposite direction. We measured the strength of this tactile motion aftereffect (tMAE) induced with different combinations of adapting and test speeds. Distal-to-proximal or proximal-to-distal adapting motion was applied to participants' index fingers using a tactile array, after which participants reported the perceived direction of a bidirectional test stimulus. An intensive code for speed, like that observed in SI neurons, predicts greater adaptation (and a stronger tMAE) the faster the adapting speed, regardless of the test speed. In contrast, speed tuning of direction-sensitive neurons predicts the greatest tMAE when the adapting and test stimuli have matching speeds. We found that the strength of the tMAE increased monotonically with adapting speed, regardless of the test speed, showing no evidence of speed tuning. Our data are consistent with neurophysiological findings that suggest an intensive code for speed along the motion processing pathways comprising neurons sensitive both to speed and direction of motion.
authors.affiliation: School of Psychology, University of Sydney, Sydney, Australia; Neuroscience Research Australia, Sydney, Australia; Faculty of Health Sciences, University of Sydney, Sydney, Australia; MARCS Institute for Brain, Behaviour and Development, Western Sydney University, Sydney, Australia; and s.mcintyre@westernsydney.edu.au.
authors.forename: S
authors.identifier: http://orcid.org/0000-0002-0544-6533
authors.initials: S
authors.lastname: McIntyre
authors.affiliation: Neuroscience Research Australia, Sydney, Australia; MARCS Institute for Brain, Behaviour and Development, Western Sydney University, Sydney, Australia; and School of Medical Sciences, University of New South Wales, Australia, Sydney, Australia.
authors.forename: I
authors.initials: I
authors.lastname: Birznieks
authors.affiliation: Neuroscience Research Australia, Sydney, Australia; School of Medical Sciences, University of New South Wales, Australia, Sydney, Australia.
authors.forename: R M
authors.initials: RM
authors.lastname: Vickery
authors.affiliation: School of Psychology, University of Sydney, Sydney, Australia;
authors.forename: A O
authors.initials: AO
authors.lastname: Holcombe
authors.affiliation: Faculty of Health Sciences, University of Sydney, Sydney, Australia;
authors.forename: T
authors.initials: T
authors.lastname: Seizova-Cajic
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D009474:Neurons / Q000502:physiology*; D014110:Touch; D055698:Touch Perception
keywords: adaptation; human; motion; psychophysics; touch
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