Tactile Research Laboratory
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| We
take for granted our ability to perceive the
external world, but how does the nervous system accomplish this
remarkable
feat? Focusing primarily on the sense of touch, our laboratory
addresses
this
question with a combination of rigorous experimental (psychophysical
testing)
and
theoretical (computational modeling) approaches. Research Themes Our research touches upon many interesting themes, including:
We employ a variety of techniques, including:
Broadly speaking, we aim to: |
 In our experimental investigations, we strive to probe tactile perception with precisely controlled stimuli. Our laboratory currently houses three sensory testing stations that we use to probe different aspects of tactile perception:
When commercial equipment does not exist for a specific purpose, we design and build novel equipment of our own. We have invented:
See our video-article: Goldreich
D, Wong
M, Peters RM, Kanics IM (2009) A
tactile automated passive-finger stimulator (TAPS). Journal of
Visualized Experiments.
28. doi:
10.3791/1374.
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The skin, the body's largest sensory surface, is endowed with a rich array of receptors that detect static pressure, vibration, stretch, temperature, and other stimulus features. We are interested in how the skin and its cutaneous receptors limit tactile acuity. For example, do people with more compliant skin have better tactile acuity? How does variation in receptor density between individuals affect performance on tactile spatial tasks? To investigate, we measure tactile acuity and skin features in the same individuals. Two skin features of interest are sweat pore density and fingertip surface area. Merkel cells, cutaneous receptors that respond to static skin indentation, cluster in the deep epidermis beneath sweat pores on the skin's surface. We have shown that index fingertip surface area predicts both sweat pore density and tactile spatial acuity, such that people with smaller index fingers have more sweat pores per square mm and finer spatial acuity. We infer that cutaneous receptors are packed more densely in smaller fingers, conferring finer spatial perception. Thus women, for instance, tend to have better tactile acuity than men. The figure above, adapted from Peters, Hackeman, and Goldreich (2009), shows high-resolution images of the index fingertips of a woman and man. Notice that sweat pores (punctate stain) are more closely spaced in the woman's finger. As fingertip surface area increases, sweat pore density decreases (lower right scatterplot) and tactile performance worsens (upper plot). Red symbols: women; blue symbols: men. See our paper: Peters R, Hackeman E, Goldreich D
(2009) Diminutive
digits discern delicate details: fingertip
size and the sex difference in tactile spatial acuity. Journal of Neuroscience 29: 15756
–15761.
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Tactile sensation (the sensorineural response to physical stimuli) begins with the receptors in the skin, but tactile perception (the interpretation of this sensorineural activity) is achieved by the central nervous system (CNS). We are interested in characterizing this central processing of somatosensory information. For example, after a sensory stimulus is received, how much time does the CNS require to create a tactile percept? Across individuals, to what extent does variation in tactile acuity reflect individual differences in central tactile processing, as opposed to variation in peripheral characteristics (see above)? One way our laboratory characterizes central tactile processing is to study how tactile perception changes upon functional reorganization of the central nervous system. For instance, in blind people, normally visual cortical areas acquire tactile responsiveness. What, if any, is the perceptual consequence of this crossmodal plasticity? When blind people learn to read Braille, the representation of the reading finger expands within the somatosensory homunculus. What, if any, is the perceptual consequence of this somatosensory plasticity? The goal of this line of research is to determine the changes in perception that may result from known changes in functional brain organization. The lab's experimental projects in this area include psychophysical studies of tactile spatial acuity and vibrotactile acuity of blind and sighted people. The figure above, from Goldreich and Kanics (2003), shows the effects on index finger tactile spatial acuity of blindness, age, and sex. See our papers: Wong M, Hackeman E, Hurd C,
Goldreich D (2011) Short-term
visual deprivation does not enhance passive tactile spatial acuity.
PLoS ONE 6(9): e25277.
Wong M, Gnanakumaran V, Goldreich D (2011) Tactile spatial acuity enhancement in blindness: evidence for experience-dependent mechanisms. Journal of Neuroscience 31: 7028-7037. Bhattacharjee A, Ye AJ, Lisak JA, Vargas MG, Goldreich D (2010) Vibrotactile masking experiments reveal accelerated somatosensory processing in congenitally blind Braille readers. Journal of Neuroscience 30: 14288-14298. Goldreich D, Kanics IM (2006) Performance of blind and sighted humans on a tactile grating detection task. Perception & Psychophysics 68: 1363-1371. Goldreich D, Kanics IM (2003) Tactile acuity is enhanced in blindness. Journal of Neuroscience 23: 3439-3445. |
 Sensorineural activity provides imprecise, often ambiguous information about the external world. A growing body of work suggests that the brain perceives amid uncertainty through a process of Bayesian inference, interpreting vague sensory information in light of prior experience to generate optimal percepts. We study tactile perception as a process of Bayesian inference. Our objectives are to create and experimentally test: 1) Bayesian perceptual models of human tactile illusions, and 2) Bayesian ideal observer models that optimally process simulated sensorineural signals, providing a benchmark against which to assess human performance on tactile tasks. In addition, in collaboration with researchers in non-tactile modalities (e.g., vision, audition), we aim to develop and test Bayesian perceptual models relevant to those modalities. The figure above, adapted from Goldreich (2007), depicts a Bayesian perceptual model that replicates a variety of tactile spatiotemporal illusions, including the famous cutaneous rabbit (sensory saltation) illusion. The perceptual length contraction formula (top center) relates the perceived distance between two taps to the skin, l-prime, to the actual distance, l, and time delay, t, between the taps. See our papers: Goldreich D (2009) An ideal observer for passive tactile spatial
perception. Frontiers in
Systems Neuroscience. Conference Abstract: Computational and
systems neuroscience. doi: 10.3389/conf.neuro.06.2009.03.058
Goldreich D (2007) A Bayesian perceptual model replicates the cutaneous rabbit and other tactile spatiotemporal illusions. PLoS ONE 2(3): e333. |
