Psychophysical Characteristics Of Roughness Sensation From Fabric Surface Texture Structures

Roughness sensation originated from fabrics’physical properties and geometry properties. When human touched fabric surfaces using bare-finger, the interaction between skin and fabric surfaces triggers neurons of cutaneous mechanoreceptors, and then the evoked neural signals were integrated, distinguished and explained by peripheral afferent fibers and central nervous system. As a primary dimension of tactile texture perceptions, roughness sensation influences the style and wearing comfortable of fabrics.In previous studies, the evaluation of fabric roughness was taken by sensory evaluation and objective test index such as SMD value by statistical method from one-dimensional profile. Unfortunately, sensory evaluation lacks of theoretical direction and this method has no generality. SMD value by KES-F tester only characterizes the average height of surface texture elements. However, roughness perception is also related to texture spacing, the size of texture element and so on according to the results of psychophysical experiments and physiological experiments from such objects as sandpapers and gratings. Meanwhile, in the field of physiological, they think human sensory system was capable of performing a spectrum analysis. This speculation has been confirmed in visual and audio field. Many researchers believe that all of individual Fourier spectral components of any surface morphology were perceived and superimposed to form an overall percept.Because fabric surfaces are flexible texture material, with different compression and multi-scale performance from hardness surfaces, the basic stimulus of roughness could not be identified leading to no a consensus on the relationship between roughness sensation and mechanical and physical properties. On the basis of the results of hardness surface tactile research, combining the results of physiological and psychological experiments, using the signal of surface morphology through KES-F tester, this thesis has done following works.(1) The Mean Deviation of the Surface profile (SMD), the texture spatial period, the maximum harmonic amplitude and the harmonic wavelength of maximum harmonic amplitude were extracted from the fabric morphology and spectrum figures. The concordance between the roughness sensation rank and the rank of each of four morphology indexes were compared. The first experiment showed that the spatial-intensive cues, i.e. the amplitude and the texture spatial periods were equivalent in scaling tactual roughness sensation of fabrics and the single spectral component was poor. (2) Human fingerprint play an important role in fabric roughness discrimination, so fabrics are divided into two parts which one is greater than fingerprint spacing (0.8mm) called coarse surface and the other is less than fingerprint spacing called fine surface according to texture spatial period. The concordance between the roughness sensation rank and the rank of each of four morphology indexes were compared respectively. The results indicated that for coarse surfaces the texture spatial period dominated in the tactual roughness judgment of fabrics with texture-patterns spacing more than human fingerprint wavelength and this results was confirmed adding more fabrics.(3) Differential threshold and Weber fraction are researched by paired comparison method for clearly understanding how these physical factors effect on roughness sensation. The results show that above-mentioned four indexes can not representation roughness sensation by itself and there are some defects using two single harmonic component indexes because of less information than other indexes.(4) In order to exploring the psychophysical function of roughness, this thesis try to establish a roughness model using the method of magnitude estimation when subjects touch fabrics and according to physiological mechanism. This model explains that relationship between received stimuli by two receptors (SAI receptor and PC receptor) and roughness sensation.In conclusion, roughness sensation of fabrics is related to the height and spatial period of texture element. It is one-side to characteristic roughness sensation with any of those indexes. Different type fabrics which depend on fingerprint width own their different roughness physiological mechanism. For coarse fabric surface, the magnitude of roughness is closely related to texture spatial period, which mainly depend on SAI receptor. However, for fine surface, roughness sensation is generated by the response of SAI receptor and PC receptor.