RF
Receptive field map of a Utah Electrode Array impinging on area 1 (top) and a Floating Microelectrode Array impinging on area 3b (bottom). We use these arrays to stimulate and record from somatosensory neurons.


When we interact with an object, much information about the object is conveyed through signals from the hand. Information about the shape of the object, its texture, its compliance, and its thermal properties is carried in the pattern of activity evoked in a variety of receptors embedded in the skin, the joints, and the muscles. We can often recognize an object simply on the basis of sensory signals emanating from our hands. Without this information, manipulating objects would be slow, clumsy, and effortful.

Combining psychophysics, peripheral and cortical neurophysiology, and computational modeling we seek to discover the aspect of the neural response that accounts quantitatively for behavior at each processing stage (nerve, area 3, area 1, area 2).

This lab is currently following four lines of inquiry:

Sensory feedback for upper limb neuroprostheses

Tactile sensation is critical for effective object manipulation, but current prosthetic upper limbs make no provision for delivering haptic feedback to the user. For individuals who require use of prosthetic limbs, this lack of feedback transforms a mundane task into one that requires herculean concentration and effort. Although vibrotactile motors and sensory substitution devices can be used to convey gross sensations, a direct neural interface is required to provide detailed and intuitive sensory feedback. In view of this, the new generation of neuroprostheses will enable electrical stimulation of somatosensory neurons in the peripheral or central nervous system.  With this in mind, we develop and test approaches to conveying the tactile information required for basic object manipulation through electrical stimulation of somatosensory neurons.

The neural basis of tactile texture perception 

Texture is the sensory correlate of surface material and microgeometry. Though textural information can be obtained both visually and auditorily, touch yields much finer and more complex textural information than do the other sensory modalities. When we run our fingers across a textured surface, complex, high-frequency vibrations are produced in the skin. We investigate how these vibrations are transduced and processed in the nervous system to culminate in a texture percept.

rf map
Spectrogram of the response of a neuron in area 3b to a sinusoidal sweep.

The neural basis of proprioception 

Interacting with our environment requires us to resolve spatial relationships. Accordingly, the brain maintains multiple representations of space, each at different scales and in different coordinate systems, all of which must interact intimately to guide action. Information about our body in space, proprioception, is key because all other neural representations of space must ultimately interface with proprioceptive representations for us to act efficiently upon objects. The movements of patients who have lost proprioceptive feedback, and thus must rely solely on vision, are consequently very slow, poorly coordinated, and require great concentration. In addition to its function in motor control, the awareness of our body and its position in space is an essential component of our sense of self. As the hand is our most important organ for grasping, tool use, and haptic exploration, we seek to characterize how hand position and hand movements are encoded in areas of the brain known to receive proprioceptive signals (i.e., areas 3a and 2).

The integration of tactile and auditory signals

We are constantly bombarded by myriad sensory signals and are tasked with sorting these for useful information about our environment. Signals conveyed by our sensory systems interact in time and space, affecting not only when and where we perceive meaningful events, but even the identity and content of these occurrences. Familiar examples of such perceptual interactions include the ventriloquism illusion (in which viewing an object biases the perceived location of a separate sound source) and the McGurk effect (in which seeing lip movements biases the perception of simultaneously heard speech sounds). During haptic exploration of surfaces, complex mechanical oscillations—of surface displacement and air pressure—are generated, which are then transduced by receptors in the skin and in the inner ear. Tactile and auditory signals thus convey redundant information about texture, partially carried in the spectral content of these signals.  In ongoing psychophysical experiments, we investigate how tactile and auditory signals are integrated to form a coherent percept.
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-- Sliman Bensmaia, Ph.D.
       Principal Investigator