Expertise:
Processing of spatial information
Both vision and touch share the common problem of inferring stimulus form and motion from a spatio-temporal pattern of activation across a two-dimensional sensory sheet (i.e., the retina and the skin). In a series of psychophysical and neurophysiological studies, we have shown that the two systems have evolved analogous neural mechanisms to process both form and motion.
Processing of temporal information
The processing of tactile vibration is in many ways analogous to the auditory processing of acoustic stimuli. Indeed, the auditory and somatosensory systems respond over an overlapping range of stimulus frequencies (from about 100 to 1000Hz) and the underlying stimulus energy is essentially identical. Furthermore, in both modalities, oscillating stimuli yield temporally patterned activity in the peripheral afferents and the evidence suggests that this patterning plays an important role in perception of both auditory and vibrotactile stimuli.
Vibrations have been shown to play a role in the tactile perception of fine textures: when tactually exploring finely textured surfaces, small vibrations are produced in the skin. These vibrations are then converted into neural signals by specialized receptors embedded in the skin and these signals convey information about surface microgeometry. Our perception of fine textures has been shown to depend on the spectral content of the vibrations they elicit in the skin, in a manner analogous to the way in which the spectral content of acoustic stimuli plays a role in the percepts they elicit. In a series of parallel psychophysical and neurophysiological experiments, we investigate the neural mechanisms underlying the tactile perception of vibrations (and, concomitantly, of fine textures).
Tactile feedback in sensorized prostheses
Neural prostheses such as cochlear, vestibular and retinal implants involve sensing the environment using artificial sensors, converting data from these sensors into neural signals, and applying a pattern of electrical stimulation to a neural epithelium designed to mimic, biofidelically to the extent possible, the signals that would have been produced by the sensory environment if the native sensory transducers were still in place. We are developing models that can predict the response of low-threshold mechanoreceptors to arbitrary vibratory stimuli presented to the surface of the skin. Using this model, then, signals transduced by sensors located on the prosthetic can be converted into desired patterns of neural activity, which can then be implemented in the peripheral nerve through electrical stimulation.
One of the barriers to developing sophisticated sensorized prostheses for amputees is our limited knowledge of the neural mechanisms that mediate proprioceptive feedback. In an attempt to fill this void, we are investigating the response properties of neurons in areas 3a and 2, which have been implicated in proprioception. This work will form the basis for providing proprioceptive feedback for amputees via cortical stimulation.
Specific research projects:
-- The neural mechanisms of tactile shape and motion perception
-- The neural mechanisms of vibration and texture perception
-- Biofidelic models of mechanoreception and tactile feedback
-- The representation of limb state in the primary somatosensory cortex
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