Graduate School of Biomedical Engineering, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia.
Neuroscience Research Australia, Randwick, New South Wales, Australia.
J Neurophysiol. 2021 Mar 1;125(3):809-823. doi: 10.1152/jn.00504.2020. Epub 2021 Jan 13.
Perception of the frictional properties of a surface contributes to the multidimensional experience of exploring various materials; we slide our fingers over a surface to feel it. In contrast, during object manipulation, we grip objects without such intended exploratory movements. Given that we are aware of the slipperiness of objects or tools that are held in the hand, we investigated whether the initial contact between the fingertip skin and the surface of the object is sufficient to provide this consciously perceived frictional information. Using a two-alternative forced-choice protocol, we examined human capacity to detect frictional differences using touch, when two otherwise structurally identical surfaces were brought in contact with the immobilized finger perpendicularly or under an angle (20° or 30°) to the skin surface (passive touch). An ultrasonic friction reduction device was used to generate three different frictions over each of three flat surfaces with different surface structure: ) smooth glass, ) textured surface with dome-shaped features, and ) surface with sharp asperities (sandpaper). Participants ( = 12) could not reliably indicate which of the two surfaces was more slippery under any of these conditions. In contrast, when slip was induced by moving the surface laterally by a total of 5 mm (passive slip), participants could clearly perceive frictional differences. Thus making contact with the surface, even with moderate tangential forces, was not enough to perceive frictional differences, instead conscious perception required a sufficient size slip. This study contributes to understanding how frictional information is obtained and used by the brain. When the skin is contacting surfaces of identical topography but varying frictional properties, the deformation pattern is different; however, available sensory cues did not get translated into perception of frictional properties unless a sufficiently large lateral movement was present. These neurophysiological findings may inform how to design and operate haptic devices relying on friction modulation principles.
对表面摩擦特性的感知有助于我们多维地体验探索各种材料的过程；我们用手指在表面上滑动以感受其质感。相比之下，在操作物体时，我们握持物体时不会进行这种有意的探索性运动。鉴于我们能意识到手中物体或工具的滑溜程度，我们研究了指尖皮肤与物体表面的初始接触是否足以提供这种有意识感知到的摩擦信息。我们使用二选一的强制选择协议，通过被动触摸，检查当两个在结构上完全相同的表面垂直或成 20°或 30°角接触固定手指时，人类通过触摸检测摩擦差异的能力。我们使用超声摩擦减少装置在三种具有不同表面结构的平坦表面上产生三种不同的摩擦：光滑玻璃、具有圆顶状特征的纹理表面和具有尖锐凸起的表面（砂纸）。参与者（= 12）在任何条件下都无法可靠地指出两个表面中哪个更滑。相比之下，当通过横向移动表面总共 5 毫米（被动滑动）来产生滑动时，参与者可以清楚地感知到摩擦差异。因此，仅仅与表面接触，即使施加适度的切向力，也不足以感知到摩擦差异，而是需要足够大的滑动才能产生意识感知。这项研究有助于理解大脑如何获取和利用摩擦信息。当皮肤接触具有相同形貌但具有不同摩擦特性的表面时，变形模式会有所不同；然而，除非存在足够大的横向运动，否则可用的感觉线索不会转化为对摩擦特性的感知。这些神经生理学发现可能为如何设计和操作基于摩擦调制原理的触觉设备提供信息。
