A multi-finger positional display (the TACTUATOR) was developed to study communication through the kinesthetic and vibrotactile aspects of the tactual sensory system of the hand. The display consists of three independent single contact-point actuators interfaced (individually) with the fingerpads of the thumb, the index finger, and the middle finger. Each actuator utilizes a disk-drive head-positioning motor augmented with angular position feedback from a precision rotary variable differential transformer (RVDT). A floatingpoint DSP system provides real-time positional control using a digital PID controller. Stimuli from threshold to about 50 dB SL can be delivered throughout the frequency range from near DC to above 300 Hz, thereby encompassing the perceptual range from gross motion to vibration. Actuator frequency and step responses are well modeled as a second-order linear system. Distortion is low allowing delivery of arbitrary stimulus waveforms, e.g., 25 mm low-frequency motion with superimposed high-frequency vibration. System noise and inter-channel crosstalk are also small. As one example of behavioral performance verification, absolute thresholds measured with the stimulator are in general agreement with values in the literature. Overall, the TACTUATOR accurately follows its drive waveforms and is well suited for a variety of multi-finger tactual perceptual studies.

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