Distribution Characteristics and Correlation of Edge Sharpness Threshold and Contact Area

It is currently unclear how sharpness discrimination ability is distributed across a wide range of edge sharpness and the effect of contact area on haptic perception. We 3D printed triangular prisms with various edge sharpness and half-edge widths in the full-scale range and conducted 2AFC tasks to gain the haptic threshold distribution. Results show that the distribution curves of the sharpness threshold and its contact area have a similar inflection point at 115$^\circ$, implying a boundary between medium-low and high stimuli. It is also found that Weber fractions in the medium stimulus range follow Weber's Law and are consistent with previous studies but lower than the mean of Weber fractions in the high stimulus range. Besides, there is no significant difference in upper and lower thresholds in the medium-low stimulus range but a significant difference in the high stimulus range with the higher upper threshold. Variations in contact area do not affect sharpness discrimination ability when the half-edge width exceeds 2 mm. However, decreasing the half-edge width from 2 mm to 1 mm significantly reduces haptic sensitivity. Our findings offer preliminary evidence contributing to understanding haptic perception in edge sharpness discrimination, encompassing the properties of objects and object-individual interfaces.