2 Information Transmission with a Multi - Finger Tactual Display

This work was motivated by our interest in using the sense of touch as an alternative communication channel for sensory substitution. Previous research has demonstrated that some deafand-blind individuals can receive conversational English at almost normal rates using the Tadoma method, in which the user places a hand on the face and neck of a talker and monitors the mechanical actions associated with speech production. To this day, however, no one has achieved a similar performance level with electromechanical devices developed for tactual speech communication. These devices typically do not engage the hand and use homogeneous vibrotactile arrays that lack distinctive perceptual qualities. In contrast, Tadoma makes use of the hand and a rich display, the talking face, that involves kinesthetic stimulation (low-frequency large-amplitude motions) as well as vibrotactile stimulation (high-frequency small-amplitude vibrations). A major goal of this research is to explore how information transmission can be improved by simultaneously stimulating both the kinesthetic and tactile components of the tactual system. A multi-finger positional display, the T ACTUATOR TM, was developed. It consists of three independent single-contact-point actuators interfaced with 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. It is capable of delivering arbitrary waveforms within an amplitude range from absolute detection threshold to about 50 dB sensation level, and a frequency range from near DC to above 300 Hz (e.g., 25 mm