Visual field magnification and touch perception when exploring surfaces with the index finger and a rigid instrument

The aim of this project was to compare texture discrimination when both touch and vision were perturbed.

Texture discrimination is important in the workplace. How textures are identified with the finger and with instruments when vision is magnified with lenses or video cameras is unclear.

Sandpaper was explored with the index finger or a metal instrument (hemostat), using normal or magnified vision. The forces generated during exploration were measured, and participants rated surface roughness.

With the finger, the perception of roughness was unaffected with magnification; with the instrument, magnified surfaces were perceived as rougher (p < .05). Forces during finger exploration were unaffected by magnification; forces with the instrument increased under magnification (p < .05).

Visual characteristics of the working field can influence the exploration and perception of materials. With the finger, mechanoreceptors that directly detect textures are activated, and with the instrument, receptors sensitive to vibrations are stimulated.

The higher forces produced when using instruments under magnification could lead to material damage. Attenuated perception of texture when exploring with tools may lead to difficulty in accurate touch perception. This could create problems in industrial tasks such as grading wool or identifying surface imperfections on manufactured materials, as well as in clinical settings such as dentistry or surgery in which instruments are used during tissue identification.