Effect of human forefinger postures of pressing on hardness identification

Abstract

Hardness identification is one of the most important tactile senses in humans. People use their hands in various ways to identify the hardness of an object. For example, acupuncturists identify stiffness in a muscle by pressing down with their forefinger held flat over the affected area. However, experimental evidence for the role of the pressing method in the identification of an object's hardness even when the same finger is used has not been shown yet. In this fundamental study, we investigated the differential threshold of hardness for different finger postures of pressing (pressing down with one's forefinger held “flat” or “vertically”) to determine the relationship between the different finger postures of pressing and hardness identification. We used seven elastic test pieces, each with a different Young's modulus, as the presented stimuli. We conducted an experiment using the constant method to calculate the differential threshold of hardness as a measure of hardness identification. The results showed that the differential threshold of hardness was higher when pressing down with a forefinger held “flat” than when pressing down “vertically” with the same force. This finding will be useful in evaluating the tactile identification of hardness in acupuncturists.

Keywords

• hardness identification
• tactile sense
• human forefinger posture of pressing
• acupuncturist
• human forefinger
• press force
• constant method
• differential threshold