On The Fabric Tactile Textures From The Principle Of Human Cognition

Tactile textures of fabric,in a narrow sense of the word,are perceived by human hand, namely fabric handle.Its space consists of multi-dimensional perceptual attributes,of which any principal dimension is called as the primary tactile texture.Tactile textures of fabric determine its quality and performance as well guide price.And then,it is considered as the key index evaluating the performance in the production of textiles and their sale.However,tactile textures of fabric are perceived by human,and the perception is affected by both its own properties and many subjective factors,involving cultural background,personal preference and personal emotion,et al.As a result,it is difficult to establish a criterion quantifying tactile textures.The status is owed to the lack of information for the physiological mechanism of fabric touch sensation,so that there are no specific and prevalent international or national standard for sensory evaluation on textiles,which leads to poor objectivity and difficult communication of evaluation results.Quantifying tactile textures of fabric is a scientific problem in the field of textile engineering.Various attempts are made to substitute instrumental testing for human sensory evaluation on fabric physical properties,and to develop all kinds of statistical relationship between principal physical variables,primary handle and total handle. However,the performance is poor in the parameterized design of new textile products. The reasons for failure in practice are that the developed models are based on statistical mathematics and classification into clothing end-use and style,and neglect the physiological mechanism of sensation and perception,which involves complex nonlinear phenomenon.Up to now,only do numbered researchers record and quantitatively analyze the evoked firing rates of cutaneous mechanoreceptors when human skin contacts with fabric surfaces,and the information for how to sense fabric properties,whether geometric or material,and tactual limitations as well,is lack.Importantly,the lack has much impact on parameterized design of fabric touch sensation.Therefore,this dissertation focuses on the primary cognitive mechanism of fabric touch sensation.By reviewing the biomechanical and electrophysiological phenomena related to paradigms of human touching fabric surfaces to extract perceptual attributes,this stuty makes a parameter-lumped and a Finite Element(FE)biomechanical model equivalent to the specific paradigm.Based on the developed models as well the recognized cognitive mechanism in human identifying and discriminating objects by touch means,this dissertation introduces and explains the tactile textures of fabric,and also discusses the underlying physiological mechanism of sensation and perception.In this sense,sensory evaluations on fabric physical properties in the filed of textile engineering are understood in the perspective of tactual cognitive science.This dissertation considers a central hypothesis that declares that the geometric and material properties of both fabric and human fingertip will significantly affect the patterns of stress and strain that are sensed and discriminated by SAI populations(the Merkel cell complex,and its transducers).Based on the hypothesis,the following specific contents are studied:Firstly,this paper reviews and classifies the existing recognition and understanding of fabric handle from the point of tactual cognition,and introduces the tactile textures of fabric,which is the basic work in the study.From the point of tactual cognition,this dissertation introduces the tactile textures of fabric and underlying perceptual attributes space,and then reviews and classifies the existing work of fabric handle within the framework of cognitive psychology and cognitive physiology.The present idea breaks out the general pursuit in mathematically improving the precision of prediction for fabric handle.Furthermore,this study summerizes the recognized physiological mechanism of human identifying and discriminating softness and roughness of objects in detail,including textiles,and the shortages of existing work are introduced in the view of tactual cognition.Thus,the general framework is established to characterize tactile textures of fabric.Secondly,a multi-dimensional and multi-level fingertip FE model is developed and validated.This study discovers that all of the homogeneous elastic half-space model and"water bed"model simulating fingertip,and the classical Hertz contact model as well,are unappreciated to simulate the case of human fingertip in contact with objects.This work chooses an efficient tool for exploring cognitive mechanism of tactile textures of fabric, involving softness and roughness.Based on a multi-dimensional and multi-level FE model,the mechanical responses of soft tissues within fingerpad to the loading displacement with a certain distribution, respectively,including uniform-distributed loading by a hard plane,curve-distributed loading by a cylinder,concentrated loading by punch and sequential loading by a"T"-bar, are validated by in-vivo biomechanical experiments and the evoked firing rates of SAI populations.Meanwhile,this work demonstrates that the phalanx bone within human fingertip plays an important role in focusing the external work on soft tissues in the vicinity of dense cutaneous mechanoreceptors underneath the maximum sensitive spot of fingerpad.It means that the elastic half-space model and the"water bed"model are inappropriate when the effect of structural and physiological characteristics of finger on tactual discrimination is involved.By subcutaneous tissues taking the place of bone, when the mechanical responses of fingerpad pressing toward fabric surfaces are predicted by the classical Hertz contact model,a significant deviation from the simulating resuts is discoveredOn the other hand,the orthotropic constitutive relationship characterizing mechanical properties of simple plain-woven fabric is proposed.By the protype of a plain woven fabric,a FE model of fingerpad contacting homogeneous compliant planes is developed,and the ability of the FE fingertip model in predicting the activated biomechanical responses is discussed.This study concludes that the deformation kinetics of fingertip pressing toward compliant planes is different from that case of hard objects.Thirdly,this work uncovers the mechanical sensitivity of tactual sensing system of human fingerpad,and the intrinsic difference between performance of cutaneous mechanoreceptors and that of instrumental testing in delecting fabric physical properties. In the view of human primary cognition,furthermore,it rectifies the misunderstanding of the relationship between human sensing discriminability and detectability of instrumental sensors in studying fabric handle.A parameter-lumped biomechanical model equivalent to the paradigm of fingerpad touching fabric between two fingers or between one finger and hard platform is developed,and the mechanical sensitivity,a variable characterizing the sensitivity of cutaneous mechanoreceptors is proposed.And then,in terms of the mechanical sensitivity, the discriminability of cutaneous mechanoreceptors in the mechanical resistance against compression(MRC)of fabric surfaces is analyzed parametrically,and the testing process of instrumental sensors in lab is comparable to the case of mechanoreceptors within soft tissues with high MRC.The work demonstrates that the mechanical sensitivity of cutaneous mechanoreceptors within fingerpad depends on the ratio of MRC of fabric to that of fingerpad.In this sense,the intrinsic difference exists between the ability of human sensing system and instrumental that in detecting MRC of fabric,so that the cutaneous mechanoreceptors of human fingerpad can't always identify and discriminate the detectable differences by instrumental sensors.In the existing studies on tactile textures of fabric,however,both of them are mistakenly deemed to be comparable. Considering the common principle of the developed parameter-lumped model,the above-mentioned conclusions can be generalized to a deep understanding of the intrinsic difference between human sensing system and instrumental that.Fourthly,the perceptual sensitivity,a variable characterizing human discriminability in evaluating the mechanical resistance against compression of fabric,is proposed,and the limitation of human tactual system is validated.The effect of typical fabric surface properties on softness sensation and the encoding pattern on fabric softness by tactile flow as well is discovered.This work rectifies the previous misunderstanding of fabric handle predicted by the existing models,and gives the shortage of current virtual rendering technique of fabric softness.Based on the active paradigm of fingerpad touching fabric surfaces for softness evaluation and the psychophysical law,the perceptual sensitivity,a variable characterizing the diseriminability of human tactual system are proposed,and its changing trend with MRC of fabric surfaces and properties of tactual modality is analyzed parametrically.The study demonstrates that the perceptual sensitivity of human tactual system is different from the mechanical sensitivity in primary cognition,and depends on both mechanical sensitivity and sensory modality.It means that the sensory estimations of tactile textures of fabric are intrinsically scattered,and should obey a certain probability distribution along the mechanical intensity continuum.In most of sensory evaluation on the handle of various fabric,however,the testing significance of their instrumental recording magnitudes or their fabric handle predicted by models are mistakenly considered as the perceptual discriminability.As a result,the developed statistical relationships between subjective and instrumental estimations with different sensitivity go against human cognition and the effect-cause theory.From the point of cognitive science,thus,this study will uncover the underlying cause leading to the poor prediction of existing models for fabric handle.Meanwhile,the effect of specific fabric surface properties on softness sensation can't be observed by the parameter-lumped biomechanical model,and then a FE model of fingertip pressing toward orthotropic woven fabric is developed.The typical physical properties of fabric surfaces,involving friction coefficient,initial compression modulus and out-plane poisson ratio,are discussed parametrically to discover their effect on cognition of fabric softness.The results demonstrate that both the initial compression modulus and the friction coefficient have a significant impact on tactual cognition of softness.And the small the friction coefficient is,the softer can is perceived by human. Furthermore,the softness is encoded by tactile flow.Thus,the virtual rendering of softness on a single physical property variable will has poor fidelity.Finally,based on the preferred or proximal stimuli of SAI populations encoding on geometrical properties of hard textures,this work validates the ability of the recognized encoding pattern on roughness in explaining the sensing process of tactile textures of fabric,and also strain energy density is the proximal stimulus to SAI populations with respect to the efficiency of human tactual system processing information from exterior stimulus.Furthermore,a model in conformation to the recognized physiological mechanism of tactual cognition is proposed to explain the relationship between physical properties of fabric,whether geometrical or material,and the proximal stimulus.This work is original,and will facilitate the development of methods characterizing fabric surface properties in conformation with human tactual cognition.By a FE model simulating fingerpad touching fabric with periodic surface textures and orthotropic mechanical behavior,this study proposes a tentative model of SAI populations encoding fabric surface properties by proximal stimulus.The focus is on the cross-interaction between geometrical and material properties in tactual cognition.The results indicate that strain energy density as the proximal stimulus to SAI populations encodes the initial compression modulus and geometrical profile features in a logistic law. And then,in the terms of the linear relationship between the evoking firing rates of SAI populations and the proximal stimulus,the dimensions characterizing fabric surface roughness sensation are at least four,namely asperity height and size,center-to-center distance and initial compression modulus.Together the above contents suggest that the limitations of whether identification or discrimination of human tactual system has been misunderstood in the existing statistical models predicting fabric handle,and the significant difference in statistic test is usually considered as the discriminable stimulus intensity by human,and the mechanical sensitivity of man-made instruments as the absolute thresholds in perception.As a result, those developed models obliterate the discriminability of human sensory system.On the other hand,for softness-hardness and roughness-smoothness of textiles,the primary cognitive pattern is different from that of hard texture surfaces and compliant objects with nearly same dimensions.The general research approach pursued in this dissertation is innovative because it seeks to bridge the gap between physiological modeling of sensory perception on fabric and its principal physical properties.With the development of specific contents,drawing upon the strengths of each model quantifies limitations of the touch modality in transforming distal stimuli(the physical properties of fabric)into proximal stimuli to cutaneous mechanoreceptors within fingerpad.This perspective may lead to an engineering performance model that would allow designers focus their efforts on critical parameters,and gain insight into more satisfied fabric products by costumers.Although the major physiological mechanisms underlying touch are well understood, many practical details of the mechanotransductive process are not yet understood well enough to quantitatively predict how people perceive stimuli at the fingertip.Furthermore, in terms of the subtle interactions between skin and object surfaces,this dissertation facilitates a deep understanding of mechanotransduction of geometrical and material properties encoded by SAI populations.