Haptic evaluation of touch: integration of tactile motion through space and time

This doctoral dissertation presents a comprehensive exploration of the representation of motion in the sense of touch, with a focus on perceptual and motor tasks, along with its implications in pathological conditions. In the introduction (chapter 1), the thesis reviews the intricate physiological processes governing tactile perception, including speed discrimination of tactile stimuli, while concurrently examining the neural correlates associated with these perceptual processes. The first study (chapter 2) investigates speed discrimination in touch, particularly in the context of slip motion, emphasizing the role of high-frequency vibrations and contact force dynamics. This line of inquiry sheds light on how the tactile system processes and discriminates slip motion velocity based on the combination of multiple cues. This study was conducted using a haptic device in which the participant applies the fingertip to a moving smooth glass surface, therefore evaluating passive tactile perception of speed discrimination. In a second study (chapter 3), significant attention is given to the clinical implications of slip motion speed discrimination in individuals with type 1 diabetes mellitus, revealing distinct pathological features and alterations in tactile perception. The device used to evaluate diabetic peripheral neuropathy is the same one described in the first study. The results of the second study were found to be significantly correlated with classic methods of evaluation of peripheral diabetic neuropathy (i.e., biothesiometer and nerve conduction studies). These findings provide valuable insights into clinical neurophysiology. Slip motion not only occurs because of the movement of an object against the skin, but also because of the active movement of the skin on a surface. This was investigated in the third study that explores the role of tactile slip motion in the control of reaching movements under physiological conditions (chapter 4). In the third study involving reaching movements a novel device was created to collect data using haptic technology. This investigation deepens our understanding of the interplay between tactile perception and motor control, elucidating how slip motion influences goal-directed movements. Methodological advancements are an important component of this thesis, with a detailed exposition of psychophysical data analysis techniques, emphasizing Bayesian modeling (chapter 5). This approach ensures rigorous examination of experimental results, yielding robust and statistically sound conclusions. Bayesian modeling was used for the analysis of psychophysical data in chapter 2 and chapter 3 Additionally, the dissertation introduces a novel haptic device designed to decouple touch from proprioception, expanding the toolkit for studying human tactile perception (described in detail in chapter 6). This device was used for the study presented in chapter 4. Collectively, this multifaceted research makes significant contributions to the neuroscience of haptics. It enhances our understanding of tactile perception physiology, offers insights into clinical applications, and presents innovative methodologies for studying human tactile perception. Future research avenues include investigating new active touch procedures, expanding clinical applications, and exploring the interplay of sensory modalities in dynamic environments.