| The research of tactile stimulation to human body from textile materials, in the traditional field of textile science, mainly involves fabric hand and tactile comfort. There are various characterization or evaluation methods for the two aspects of fabric performance, including physical method, psychological method, and physiological method. Previously, many meaningful results were gained by using these methods, especially for measuring and evaluating the physical properties, which had achieved systematic conclusions and normative characterization methods. However, because of the limitation of the traditional research techniques, we have not made breakthrough progress for the physiological characterization of human perception for fabric stimulation, which is the most direct characterization in fabric tactile comfort, and not formed targeted and effective research methodologies. The technology of functional Magnetic Resonance Imaging(fMRI), developed in the 90 s of the last century, brings hope for solving the problem. The most fundamental results of the brain responses can be gotten by using the advanced technology fMRI. In this thesis, the technology was introduced into the research field of fabric perception and comfort. Using fMRI, the brain responses for the physiological perception were observed when the skin of individuals was stimulated by fabric touch. In this way, human perception for fabric tactile stimulation was studied and characterized neurophysiologically, which provided direct and intrinsic results for characterizing fabric hand and tactile comfort quantitatively.People usually evaluate and judge the quality of fabrics by touching them with hands, commonly the palm of the hand which belongs to glabrous skin, but in practical use, fabrics, especially used for next-to-skin clothing and bedclothes, contact with the hairy skin of the human body in most cases. In order to study the similarities and differences of tactile perception for fabric touch on the two kinds of skin, brain responses were observed using the technology of fMRI, when forearms(hairy skin) and palms(glabrous skin) of the hand of subjects(nine male volunteers) were stimulated respectively by the friction of two kinds of fabrics, silk and linen. Then the brain fMRI data of the subjects were processed using SPM(Statistical Parametric Mapping) and several other data processing tools. The results show that, whatever for silk or linen fabric touch, there were more activations in somatosensory brain areas for palm stimulation, while more activations in emotional or affective areas for forearm stimulation. It is interesting that the deactivation results was opposite. That is, there were more deactivations in emotional or affective brain areas for palm stimulation, while more deactivations in somatosensory brain areas for forearm stimulation. The meaning of deactivation is that the normal brain activities in the brain area are restrained. Therefore, the fMRI results suggest that, if we want to study the sensory perception for fabric physical performance(e.g. fabric parameters related to fabric hand), it is better using fabric stimulation to the glabrous skin, and if we want to research the emotional or affective perception for fabric touch(e.g. tactile comfort), it is better using fabric stimulation to the hairy skin.For further demonstrating the above conclusions and inferences, the brain cognitive mechanisms and the quantitative representation for fabric hand and tactile comfort were investigated in the dissertation. The main characteristic values are the intensity and the extent(the number of activated voxels) of activation, which can be used to quantitatively characterize the value and the sensitivity of the brain perceptions for fabric hand and tactile comfort.As for the investigation of tactile comfort, the brain activation results of forearm stimulation from silk and linen fabric show that, compared with linen fabric, when the forearm skin of the subjects was stimulated by friction touch with silk fabric, in the posterior insula cortex, activation intensity was higher which was 1.2 times of linen fabric stimulation, and the number of activated voxels was more(1.7 times). The brain activities in the posterior insula cortex are very sensitive for emotional or affective perception, so it can provide an important reference for the investigation of fabric comfort.As for the investigation and the characterization of the brain perception for the physical attributes related to fabric hand, another experimental study was performed. Firstly, the physical properties of the two fabrics, silk and linen, were measured using KES instruments. Then, eight subjects were required to touch silk fabric and linen fabric respectively with their fingers, and at the same time, the brain responses were observed in situ using fMRI. Finally, the subjects compared their subjective perceptions for touching the two fabrics. The subjective results show that, by all of the subjects’ opinion, the silk fabric felt softer(or more pliable), more slippery and glutinous(or waxy), and less coarser than the linen fabric, which are complete in accord with the KES results. The fMRI results show that, whatever silk or linen fabric, there were obvious activations in the contralateral brain areas of somatosensory cortices, including the primary somatosensory cortex(SI) and the secondary somatosensory cortex(SII), and motor cortices, including the primary motor cortex(MI) and the secondary motor cortex(MII). In addiition, some voxels in posterior insula cortex and Broca’s Area(with functions linked to speech production and language comprehension) were also activated in the experiment. By comparison, the activation difference for the two fabric stimulations was not distinct in the brain area of SII, however, the activation intensity and activation extent in SI and motor cortices were larger for the result of silk fabric stimulation than linen fabric stimulation. In detail, in the area of SI, the activation intensity and extent of silk fabric stimulation are 1.14 and 2 times than that of linen fabric, and in motor areas, the multiples are 1.12 and 2.73 times respectively.Combining the fMRI results with the physical parameters results(measured using KES) of the of the two fabrics related to fabric hand, as well as the subjective evaluation results(collected with psychological questionnaire), in the dissertation we analyzed and discussed the cognitive mechanism of the human brain for various physical properties of fabric, and inferred the brain functional regions for perceiving fabric softness, roughness, and surface glutinousness. It is suggested that the characteristic brain region related to the macrophysical properties of fabric may be the primary somatosensory cortex(SI), while the functional brain area for perceiving the microphysical properties of fabric is likely to be the secondary somatosensory cortex(SII), especially the subregion OP1. Because the silk fabric felt more pliable, there were more activations in SI. Both the glutinous property of silk fabric and the coarse property of linen fabric evoked activation in OP1, so there were little activation difference in OP1 between the two fabrics. In addition, activations in motor corteice, especially in the secondary motor cortex, can provide references for the characterization of the stimulation of some surface properties of fabric, suce as glutinousness.Then, in order to verify the above inference and further analyze the response difference of the brain in the above two areas, the method of ROI(region of interest) analysis was used to calculate the brain signal changes in the above related brain regions. The results show that, compared with touching linen fabric, when subjects touched silk fabric using fingers, the percent signal changes in the two brain regions of SI and OP1 were larger, in detail, 1.25 times in SI and 1.75 times in OP1, which had verified the above inference and conclusion. The brain signal change in OP1 show that, the stimulation of the glutinousness of silk fabric evoked greater response in OP1 than the coarseness of linen fabric.Finally, in the end of the dissertation, we summarized the problems existing in the procedures and the results of the fMRI experiments, and proposed some representative fMRI experimental paradigms which are fit for investigating the cognitive behavior of the brain on fabric stimulations, such as the selection principles of the fMRI experimental design methods, the skin sites of the human body stimulated by fabric touch, and so on. These paradigms can provide references of experimental methods and characterizing techniques for studing the brain cognition on fabric hand(focusing on the physical properties of fabric) and tactile comfort(focusing on the emotional information in the perception of fabric touch). |
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