The Cutaneous Communication Laboratory at Princeton

Vibrotactile Stimulators and Arrays
    The research of the Cutaneous Communication Laboratory has implications for the development of sensory aids for deaf, blind, and deaf-blind persons, and also for those interested in perceptual processes per se. Our aim is to help those people developing devices for sensory impaired people using the skin as the alternative input medium. We do basic research that illuminates how information can be best transmitted through the skin. Our research questions range from the simple ("How intense must a vibration be for you to feel it?") to the complex ("What mechanisms account for the mistakes that people make when trying to identify letters of the alphabet presented close together in time?"). Our experiments involve presenting patterns through contactors that touch the skin. The patterns are produced by the movement (vibration) of the contactors creating a buzzing sensation. This laboratory has had a long-standing interest in both basic and applied research projects. The majority of basic studies with single-site stimuli have used Bimorph or Bruel & Kjaer tactor systems. More complex displays have used the arrays from devices such as the Optacon© and the Tactaid-7© to explore the individual differences in tactile pattern processing. We have also been involved in the development and evaluation of new display technologies, such as Sensor Electronics' (Medford, NJ) MTAC high-density array and their Roto-Oscillating Crown tactor system, as well as the Tactile Situation Awareness System (TSAS) with the Naval Aerospace Medical Research Laboratory in Pensacola FL. Recently the efforts of the Cutaneous laboratory have concentrated on examining the individual differences in tactile pattern perception, particularly in older persons, and whether it might be possible to predict success with such devices based on the individual's sensory, perceptual, or cognitive abilities.


The single-contactor workhorse in our laboratory is the Bruel & Kjare 4810 minishaker. It is a very expensive but powerful system for presenting vibration to a single site over the frequency range that commonly is used in the majority of psychophysical testing (10-400 Hz). In our system, the actual contactor that touches the skin is a 7-mm diameter PCB 303A accelerometer (see below) that is mounted on the driving element of the mini-shaker. The minishaker is driven with a B&K 2706 amplifier. The package of amplifier and shaker, these days, probably costs in the neighborhood of $4000.


.....Bruel & Kjaer Instruments Inc......Phone: (508) 481-7737
.....185 Forest Street.......................FAX (508) 624-0503
.....Marlbourough, MA 01752-3093..............Bruel & Kjaer Home

The most common tactor systems in our laboratory use piezoceramic bimorph benders. We have used these in beam (clamped at one end) configurations. Often the free end has a plastic hemispher contactor that strokes the skin (as in our larger 2-dimensional arrays (Cholewiak, R. W., & Sherrick, C. E. (1981). A computer-controlled matrix system for presentation to the skin of complex spatiotemporal patterns. Behavior Research Methods & Instrumentation, 13, 667-673.)) or, in our more recent work with linear arrays, the free end has a contactor on its surface that produces a perpendicular tapping against the skin. There are a number of manufacturers, although the one we have had the most recent contact with is Piezo systems. They have a variety of sizes of benders in stock, and sell at reasonable prices, even using a credit card. The sizes that we often buy are in the 30 x 10 mm range, and sell for $20-$30 each.


.....Piezo Systems, Inc.......................... Tel: 617 - 547 - 1777
.....186 Massachusetts Avenue..................FAX 617 - 354 - 2200
.....Cambridge, MA 02139.......................Piezo Systems Home Page

Other potential sources for piezoceramic benders include Active Control Experts, Inc., 215-T First Street, Cambridge, MA 02142-1227, Phone (617) 577-0700, Fax (617) 577-0656, and TRS Ceramics, Inc.


A new type of piezoelectronic actuator, which is apparently stronger and more rugged than traditional piezoceramic benders, is offered by the Face International Corporation, 427 West 35th Street, Norfolk, VA 23508, Phone (757) 624-2121. The actuators are being marketed under the name THUNDER.


The hearing aid connectors that are very useful for such small applications can be purchased for about $15 each from:


.....Plastics One, Inc.................Phone: (540) 772-7950
.....P. O. Box 12004..................FAX (540) 989-7519
.....Roanoke, VA 24022-2004.........................................

In many of our piezoceramic bender applications we have used semiconductor strain gauges mounted (glued) on the bender to monitor the displacement amplitude and waveform under load. The source we've used for our strain gauges is BLH:


.....BLH Electronics, Inc.......Phone: 617-821-2000
.....75b Shawmut Road..................800-247-2454
.....Canton, Mass. 02021.........FAX: 617-828-1451 ................BLH Home or SR4 strain gauges.

They have two lines of gauges in their SR4 products - foil, or semiconductor. There is about a 5 or 10:1 price premium for the semiconductor gauges and are much more fragile, but they are also more sensitive. Talking recently to their representative, they appear to be the only manufacturer of semiconductor strain gauges. Period. Since it's been a number of years since we've ordered from them, I'd call to get advice regarding the best unit to use - I'm sure the technology has advanced greatly. These can be glued directly to the bender and a simple battery-powered circuit allows us to monitor the change in voltage read with a voltmeter and converted to displacement (under load) after calibration. We typically calibrate visually as well as with an accelerometer, depending on the ease with which we can visualize the contactor. There are several sources for accelerometers. Although Bruel & Kjaer have an extensive line of accelerometers and force sensors, we have been very happy with the units we have purchased from PCB Electronics:


.....PCB Electronics...............Phone: 716-684-0001
....3425 Walsh Avenue............FAX: 716-684-0987
....Depew, NY 14043....................sales@pcb.com ..........PCB Home or PCB technical support.

Revised 03/14/99