James C. Craig - US grants

The objective of this project is to understand how tactile patterns are perceived by human subjects. The project will focus on the processing of spatiotemporal patterns and the interactions that occur between spatial patterns presented to the same and to separate locations. The results from the psychophysical measures will be related to neurophysiological studies of peripheral and central responses to tactile stimuli. The tactile patterns will be generated by several types of displays. One of these is the dense array which consists of 400, independently controlled tactors. This display will be used to generate and test subjects' sensitivity to drilling, sinusoidal spatiotemporal patterns of various wavelengths and frequency. The array will also be used to activate selectively different populations ofmechanoreceptors. The effect of such variables as contactor penetration, velocity, and site of stimulation on spatial and intensive sensitivity will also be measured. Using the dense array as well as arrays from the Optacon, a reading aid for the blind, temporal interactions such as masking, response competition, and temporal integration will be examined. The project will also be concerned with the effect of pattern movement on interactions between tactile stimuli and between tactile and visual stimuli. One of the aims of the project is to compare results obtained with tactile stimuli to studies conducted with visual and auditory stimuli. The results from these projects will be relevant to the development of cutaneous communication systems for the deaf, blind, and deaf-blind. The results will also be relevant to the effects that intermediate surfaces such as surgical gloves have on tactile sensitivity and to the measurement and understanding of neurological problems.

The proposed research will investigate the perception of tactile patterns by human subjects. The tactile patterns will be generated on arrays of stimulators that fit against the subject's fingertips. Each array consists of 144 stimulators arranged in a matrix 6 columns by 24 rows. Sets of patterns differing along such dimensions as location, intensity, number of line segments, and so forth will be generated and presented to subjects. Response measures will include identification, discrimination, reaction time, and pattern matching. Three aspects of tactile pattern perception will be examined: masking, interactions among multiple sites of stimulation, and the role of experience. A temporal masking paradigm will be used to see how the perception of tactile patterns is interfered with by tactile maskers and how the nature of the interference changes with changes in the type of masker and in the temporal separation between target and masker. In the studies of interaction among multiple sites, patterns will be presented to as many as three sites on the fingertips and palm. This paradigm will be used to assess the role of attention in tactile information processing. The role of short-term experience will be examined by measuring changes in pattern perception as subjects learn to identify and discriminate tactile patterns. The effect of long-term experience will be evaluated by comparing the performance of groups of subjects who differ in the amount and nature of their experience with complex tactile patterns. One group will be Optacon users, blind individuals who can read by means of a tactile array. The other groups will be blind individuals without Optacon experience and several groups of sighted subjects with varying amounts of tactile experience. The proposed research will be concerned with drawing parallels between tactile processing and visual and auditory processing, with developing measures relevant to understanding the neural coding of tactile patterns, and with improving cutaneous communication systems for the blind, deaf, and deaf-blind.

DESCRIPTION (provided by applicant): In this application we combine the efforts of two long term studies investigating the neural mechanisms of tactile spatial perception. Dr. James Craig of Indiana University will not be renewing his grant but instead will be joining this project at Johns Hopkins University. The broad goals of this application are to understand how two-dimensional shape, texture and motion are represented in somatosensory cortex. Shape, texture and motion are important in all sensory systems. We will use a 400-probe stimulator that can produce a wide range of dynamic patterns to stimulate the finger pad. We will perform both psychophysical studies in humans and neurophysiological studies in non-human primates. The first aim is to understand how complex patterns are perceived and represented in somatosensory cortex. In these experiments we will investigate how spatial features such as lines and curves are combined both spatially and temporally to from complex spatial patterns. The second aim is to investigate how texture is represented in somatosensory cortex. In these experiments, we will use a wide range of spatial patterns that we used previously to study the peripheral mechanisms of texture perception to determine how texture is coded in cortex. The third aim is to investigate how motion is represented in cortex. In particular we will scan various spatial patterns across the finger pad at different directions and scanning velocities to determine how motion interacts with form and texture processing. The results from these studies will provide an understanding of the mechanisms underlying central neurological problems and will provide an understanding of the sensory feedback that is necessary for the control of prosthetic limbs. A third benefit is that these studies will aid in the development of cutaneous communication systems for the deaf and blind. PUBLIC HEALTH RELEVANCE: The results from the proposed studies will aid our understanding of the effects of both peripheral and central neurological problems, and our interpretation of the results of neurological examinations, such as changes in light touch thresholds, spatial acuity, and directional sensitivity. To provide sensory feedback for the control of prosthetic limbs, it is important to understand how the hand normally processes touch information. In addition, the proposed measures of the perceptibility of tactile patterns will aid in the development of cutaneous communication systems for the blind, deaf, and deaf-blind.