Neural Mechanisms of Tactile Perception and Object Recognition

The human hand is specialized for prehension, manipulation, and the perception of objects and their properties. When we manipulate an object, we readily perceive its texture, form, size, temperature, mass, and even its properties beyond those in direct contact with the hand (e.g., we easily perceive whether a rod held in the hand is 6" or 6' long). If the object is a probe or a tool, our perception extends to objects contacting and acting on the object held in our hand (e.g., the texture of a surface contacted by a rod). The richness of our tactile sensory experience is based on 14 different kinds of sensory receptors innervating the skin, muscles, and joints of the hand.

A principal objective of our laboratory is to understand how information from all of the sensory receptors is integrated in tactile perception. Combined psychophysical and neurophysiological experiments in this and other laboratories have shown that each of the 14 receptors types is responsible for a distinctly different aspect of tactile perception and that, taken together, these 14 aspects of perception account for the whole of tactile perception. We now concentrate on the neural mechanisms of form and texture perception.

The regions of the body with high spatial acuity (fingers, lips, and tongue) are served by neural mechanisms specialized for processing information about object form and texture. The human ability to read Braille is a prime example of the human capacity for tactile form perception. The ability to reach into a pocket and retrieve a key among a lot of coins is an example of tactile object recognition. These abilities are based on high-resolution, isomorphic neural images formed by mechanoreceptors in the skin and transmitted to cerebral cortex. In cerebral cortex, these neural images are analyzed to produce information about the form, texture, location, and motion of the object. Our research concentrates on how this is done. In psychophysical experiments, we investigate the human ability to identify and discriminate form, texture, location, and motion. In neurophysiological experiments we investigate the cerebral neural mechanisms that underlie these abilities. In theoretical and computational studies, we investigate and test models relating the neural activity to perception.

Cortical neural mechanisms of tactile perception

Tactile perception is based on information supplied by 14 different kinds of receptors in the hand. The current thinking is that the information supplied by these different receptors is kept separate in the brain until very late in the processing chain leading to perception. It makes sense that this should be so. For example, the neural computations required to extract the three-dimensional form of an object are very different from the neural computations required to determine the motion or texture of an object. There are eleven cortical areas specifically devoted to processing tactile spatial information and many more devoted to the integration of tactile information with information from the other senses. Our objective is to determine how the different tactile information processing tasks are distributed among these areas. We concentrate particularly on the neural mechanisms of form and texture perception and the roles of each of the cortical areas. The potential role of neurons in each cortical area is examined by recording the neural activity in each area while presenting a wide range of complex spatial stimuli that have previously been used in human psychophysical experiments. The neural activity in each cortical area is linked to the psychophysical data through computational models and through analyses of the neural coding mechanisms that might account for perception.