The tactile system is highly complex. The properties of its central and peripheral components determine the way external stimuli are transformed into perception. At the very first stage, first-order tactile neurons respond to skin mechanical deformation and their activation convey a representation of the sensed object (i.e., encoding). However, there are several open questions regarding which factors can significantly influence the peripheral neural response and hence, perception. The goal of the work presented in this thesis is to provide new evidence about the link between skin properties, object’s characteristics, first-order tactile neurons response and discriminative judgments.
Chapter One provides an overview of the tactile system with a focus on the peripheral components (e.g., skin, first-order tactile neurons), as well as a summary of the relevant behavioural findings on tactile perception in Young and Elderly. Chapter Two outlines the methods used in this work including psychophysics, a device to present tactile stimuli in a controlled fashion, skin measurement techniques, and manufacturing of fine-textured stimuli. Chapter Three provides an in-depth review of computational models that simulate the response of first-order neurons and how they can be applied for psychophysical research. Chapter Four is the first empirical chapter that evaluates the effects of skin and mechanoreceptive afferent properties on spatial tactile sensitivity in young and elderly participants assessed with the 2-point discrimination task. Chapter 5 is the second empirical chapter that investigates the effects of the interaction between finger and surface properties on the detection sensitivity for a single microdot in young participants with active exploration.
Chapter Six summarises the findings of the research undertaken in my doctoral studies and discusses their implications for understanding the sensory mechanisms underlying tactile perception. Overall, the findings presented in this thesis suggest that the progressive loss of mechanoafferent units contribute to the decline in tactile spatial acuity as predicted by a population model of the afferent response, and provide new evidence on the complex effects of frictional changes and the role of skin biomechanics on the detection of a microdot
