| The tongue is one of the body's most sensitive tactile sites and its high conductivity has been proven to be convenient and useful for sensory substitution/augmentation through electrotactile stimulation. Although there is evidence of tongue's electrotactile stimulation advantages, applications have been limited to provide only on/off spatial information. This dissertation aimed to contribute to the knowledge of perceptual characteristics of intensity and spatial attributes of electrical stimulation on the tongue, which may allow for more enriched coding for sensory substitution/augmentation applications.;This goal was accomplished in three studies in which right-handed naive subjects were stimulated on their tongue's dorsum and were asked to give perceptual responses following well-established psychophysical methods. In the first study, subjects selected a greater dynamic range from barely detectable to maximum without discomfort than other body's tactile sites, even with a slight drift after prolonged exposure. Within and along this range, subjects perceived small intensity differences slightly better than when estimating their absolute levels. In the second study, subjects' average minimum intensity contrast between grating bars of several spatial periods and orientations was similar to first study's intensity difference sensitivity. Larger spatial periods did not improve minimum bar contrasts. Also, lower contrasts were found for the anterior-posterior orientations and when high-intensity bar shifts were towards the anterior-right portion of the tongue. Finally, in the third study, subjects identified anterior-posterior oriented gratings better than medial-lateral and oblique orientations in a similar manner for medium and maximum bar contrasts with only a short-term improvement within the session.;The results indicated a strong contribution of rapid adapting afferent responses at the periphery for intensity differences and contrast perception and cortical processing for intensity estimation and orientation identification tasks. It was found that sensitivity on the tongue is heterogeneous and anisotropic. These studies also indicated that even with little to no experience/practice and tongue's sensitivity heterogeneity and anisotropy, subjects could perceive intensity and spatial attributes delivered electrically through the tongue. Overall this dissertation shows the great potential of tongue's electrotactile stimulation to characterize the tongue's tactile system and to utilize its sensitivity advantages to enhance clinical and sensory substitution/augmentation applications. |
