The Cutaneous Communication Laboratory at Princeton

   Founded in 1962 by Professor Frank A. Geldard (right) and Dr. Carl E. Sherrick, the Cutaneous Communication Laboratory has been at Princeton University for over 40 years, studying basic and applied problems related to how the skin processes patterns.  The Laboratory was an outgrowth and continuation of work begun at the University of Virginia by Prof Geldard under the "Virginia Cutaneous Project," that was active from the 1940's until the move to Princeton in 1962.  Dr. Roger Cholewiak, the most recent Principal Investigator, arrived from the University of Virginia in 1974 to work with Drs. Geldard and Sherrick.  Prof. Geldard, Director of the Laboratory until his retirement in 1972, passed away in 1984.  Frank Finger, Dr. Geldard's colleague at the University of Virginia, and Dr. Sherrick wrote his reminiscences and obituary.  Dr. Sherrick, Geldard's student and colleague, was Director of the Laboratory from 1972 to 1991.  He wrote a brief autobiography for a celebration at one of his former institutions, the Central Institute for the Deaf, in St. Louis, MO.  He passed away in 2005.  Upon the end of the 37th year of support under PHS/ NIH Grant NSR01-DC00076-37 through the National Institutes of Deafness and Other Communication Disorders, Dr. Cholewiak retired and closed the laboratory at Princeton. 

During the early years of the laboratory, the emphasis of the work was on cutaneous languages, particularly employing vibrotactile presentations.  Starting in the 1970's, research with stimuli presented on 2-dimensional vibrotactile displays for communication in sensory disability as well as in sensory augmentation became increasingly dominant in the laboratory's work.   In addition, after Geldard and Sherrick's discovery of the phenomenon, a considerable amount of effort was spent on study of sensory saltation in the tactile, visual, and auditory sensory modalities.

A wide variety of tactile displays have been used in the laboratory. Currently, the systems include a number of single-contactor displays based on Bruel & Kjaer 4810 shakers, Goodmans V-47 vibrators, as well as individual piezoceramic Bimorph benders. These stimulators, combined with monitoring systems based on accelerometers and displacement sensors, have allowed us to accurately examine a number of types of tactile sensitivity, including vibrotactile thresholds, growth of vibrotactile magnitude or loudness, spatial summation, pulsatile rate discrimination, and localization of stimuli as a function of frequency. Many of these have been examined in large populations of observers, including both college-age students as well as younger and older individuals. Furthermore, we have had a tradition of examining such capabilities at different body sites because of the variation that exists over the surface of the body in receptor type, tactile sensitivity, and other characteristics. In addition to the relevance of this approach to a basic understanding of the encoding processes in the skin, we have to be cognizant of the differences that have been identified when designing a device for a particular skin locus.

We have also used these types of stimulators to examine several tactile illusions, such as Tau, Phi (or apparent movement), and sensory saltation (the "Rabbit"). The saltatory illusion was discovered in this laboratory in 1972. Given certain parameters, taps at two different locations can produce a vivid sensation of taps distributed between the two sites. We continue to be one of the few sites familiar enough with the paradigm to be able to apply it in a number of sensory modalities, including vision, audition, as well as touch.

The work of the laboratory has included studies done with two-dimensional piezoceramic displays, tactile arrays that were designed to fit a number of body sites ranging from the abdomen, back, or thigh, to the palm and fingerpad. The design of such displays must take into account a number of factors, particularly the varying intensitive, spatial, and temporal sensitivity of such sites. For example, the square 8 X 8-element large array is built with large benders on 15-mm centers with a continuously variable surface contour allowing as much as 5 cm height difference between edge and center contactors. These features conform to the low vibrotactile sensitivity, poor spatial acuity, and severe topography of sites such as the thigh or abdomen. At the other extreme, a 16 X 16-element array in which the 256 contactors are contained within a 1-cm by 2-cm area is also available. The density of this array (the Multipoint TACtile array) is twice that of the more commonly-used array in this laboratory, the Optacon. Both the MTAC and Optacon systems, because of their low stimulus amplitudes and high densities, are most appropriately used to examine pattern perception on sensitive sites such as the fingertip. Currently, 3 Optacon laboratories are in operation with varying capabilities, including a system designed to allow for the study of pattern perception in the presence of competing stimuli (in a number of sensory modalities) in paradigms such as adaptation or masking, particularly with stimuli such as tactile dynamic noise that mimics environmental static. A fourth Optacon laboratory provides for simultaneous stimulation with one of the larger arrays at a different body site to allow us to directly compare patterns at the two locations as well as to examine interactions between them. Target tracking on these displays has been examined, as well as a wide variety of complex static and dynamic pattern perception tasks.

More recently, the work of the laboratory has been particularly focused on examining individual differences in vibrotactile pattern perception. For example, in a population as homogeneous as the student body of Princeton University, we have found profound differences in performance on tasks as apparently simple as learning to identify the difference between a pair of spatial patterns presented on the Optacon display. These two patterns may be correctly identified within 5 trials by some students, while others may serve in 1000 or more trials and still be unable to tell the difference between the two. We have observed similar variability when these and other patterns have been masked with dynamic tactile noise, similar to that produced by noisy electronic systems. Recent work has been extended to other subject populations including a small number of children and a larger population of older individuals. In the process of working with older observers (senior citizens from the area), a number of remedial training regimens that appear to provide the kinds of strategies that such individuals need to be able to identify and discriminate among tactile patterns have been developed. Furthermore, a battery of tests has been designed to provide predictive tools to determine whether a particular individual might be able to accurately process tactile pattern sequences of rapidly-changing streams of information. These tests include measures of ability, personal characteristics, as well as of sensory and perceptual capabilities that range over the spectrum of cognitive capacities.

One measure that appeared to play a major role in individual performance on vibrotactile pattern perception tasks was the spatial acuity threshold for the individual. This finding highlighted a research question that has not be addressed directly - What is the spatial acuity of the skin to vibrotactile patterns? Although spatial acuity of the skin has been explored with pressure stimuli, there have been few attempts to study acuity for patterned vibratory stimuli of the type used in tactile devices for augmenting communication. Such systems include speech-reading aids used by persons who are deaf (e.g., the Tactaid, placed on the forearm or abdomen), reading machines for persons who are blind (the Optacon, used on the fingertip), and spatial orientation systems used by pilots or astronauts (the TSAS, on the trunk). In every case, vibrotactile spatial acuity has never been empirically determined at the application site. Yet these devices often use spatial features (location on the array) to define the information to be transmitted. The reasonable question can be asked whether the poor transmission rates typically seen with such systems might be improved if the resolutions of the displays were better matched to the spatial acuity of the skin at each site? Currently, the effort of the Laboratory is focused on two projects that explore spatial acuity and localization ability for vibrotactile stimuli. Studies are examining localization with well-controlled stimuli on body sites used by wearable tactile communication aids and research devices. Because it is likely that stimulus parameters such as vibration frequency might affect localization, these is varied. Vibratory spatial acuity on each site is being explored by manipulating the spatial resolution of the arrays while measuring spatial pattern perception. Acuity at a site is defined by the minimal tactor separations that produce criterion performance. Because tactile aids should be usable throughout a person's life span, but particularly in the later years, older persons are participating in this study of the spatial aspects of tactile pattern perception. Practical reasons for explorations of aging effects on tactile sensitivity emerge when considering that this sensory modality may be called into play to aid individuals whose other senses have become disabled. In the working population (ages 21-64), 44% have some level of difficulty seeing, while 64% have hearing problems, and over 2.5 million people are either deaf or blind (McNeil, 1997). Important for this application is the fact that the proportion of the population who are deaf increases dramatically for those over the age of 60 (Fozard, 1990), while 88% of visually disabled persons are over the age of 60 (ANSI, 1982; CENSUS, 1991; Gill, 1993). Consequently, information on the capabilities of the touch sense in the older individual is of crucial importance, since it may be the only alternative system available to supplement remaining sensibility.