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Title: Neuropsychological mechanisms of fabric touch sensations
Authors: Liao, Xiao
Degree: Ph.D.
Issue Date: 2015
Abstract: The ultimate purpose of this Ph.D. research is to reveal neuropsychological mechanisms of fabric touch sensations by carrying out a systematic study on the process of human tactile sensory perception from physical detection of stimuli, neurophysiological coding and conduction of neural signals, and psychophysiological decoding and formation of sensory perceptions. By uncovering the neuropsychological mechanisms, the underlying grounds of fabric tactile comfort are disclosed. The primary physical stimuli generated form fabric physical properties are identified and transformed with computational algorithms to express how they impact final perceptions, which advance current understanding of human tactile perception of textiles. The research findings can provide guidance for fabric innovation, product development and e-fashion business applications like on-line certificating product tactile comfort performance. Detection mechanism of physical stimuli was studied by characterizing physical properties of fabrics using "Fabric Touch Tester" (FTT for short), which was designed and engineered for simultaneous measurement on fabric thermal and tactile properties according to the several types of human haptic sensations. The biomimetic neural signals obtained from the measurement of fabric physical and mechanical behaviours using FTT provide multi-channel physical stimuli information for analysing the thermal, surface texture and softness sensory properties of fabrics. Neurophysiological coding and transduction of the biomimetic neural signals were investigated by extracting three main types of physical stimuli according to the neurophysiological mechanisms of human skin receptors identified from literature, including thermal stimulus, surface stimulus, as well as force stimulus when deforming the fabrics. The neural coding models of each stimulus reported in neuroscience literatures were modified with consideration of the unique heterogeneous features of textile materials. Several neural responses calculation models were subsequently developed to transform fabric physical properties recorded into skin neural receptor responses. Dynamic thermal responses and mechanical behaviour of fabrics during deformation were analysed according to different stages of neural responses to calculate thermal and force neural indexes. Meanwhile, neural indexes were derived to characterize surface roughness of fabrics according to signal patterns generated from their complex surface properties.
Psychological discrimination of fabric touch sensations from human subjects was examined. Subjective measurements followed standard AATCC Evaluation Procedure 5. Experiment was designed to involve subjects in six climatic conditions and both active and passive haptic evaluation methods. Principle component analysis was performed to extract independent factors from ten sensory descriptors. Three key independent sensory dimensions, named smoothness, softness, and warmth, were derived. They matched well with the three types of physical stimuli. Statistical analyses on subjective results were conducted. Results show significant differences between passive and active touch methods, as well as between different climatic conditions. Psychophysiological study indicates as that active touch method would allow skin to receive more information than passive one due to the anatomical distribution of varied skin receptors and active manipulation of fabrics. It is also found out that acclimation to climatic condition can modify the sensitivity of subjective sensory perception and subsequently induce changes in fabric touch sensations. Underlying connections between the primary physical stimuli and final psychological perceptions were explored to obtain a complete picture of the process of human tactile sensory perception. Psychophysical relations were explored first by using correlation and regression techniques and further by applying different theories of psychophysical laws. The results show that there is no signal universal psychophysical law applicable for all the tactile sensory perceptions. For different tactile sensory perception, different psychophysical law fits better. It is also observed that interactions between different physical aspects on a single sensory dimension should not be neglected. The integrated sensory perceptions fit with the experimental observations the best by a combination of different equations derived according to different psychophysical law for individual sensations. This finding proved the hypothesis of the need of simultaneous measurement of fabric physical and mechanical behaviors. Neuropsychological mechanisms were revealed by examining the relations between neural indexes and psychological perceptions. It is concluded that the "Smoothness" was solely affected by the weighted power of PC fiber responses to stimuli with different intensity and frequency; "Softness" is affected by both the SA1 fiber responses to fabric's resistant force of bending deformation and surface-induced PC fiber responses; "Warmth" is affected by both the maximum and steady thermoreceptor responses and the SA1 fiber response to fabric's resistant force of compression deformation. Neuropsychological prediction models were developed on the basis of these findings. Models were validated by using the subjective sensory evaluation and physical measurements of a new set of fabrics. The results show that predicted touch sensations from the neuropsychological models are more closely related to subjective obtained scores than those from the psychophysical models. In summary, this Ph.D. study has generated original research findings that reveal the neuropsychological mechanisms of fabric touch sensations. These findings advance our scientific understanding on fabric tactile sensory comfort and provide a novel neuropsychological approach for sensory engineering of textile materials and products.
Subjects: Touch.
Textile fabrics -- Physiological aspects.
Hong Kong Polytechnic University -- Dissertations
Pages: xxxi, 324 pages : illustrations (some color)
Appears in Collections:Thesis

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