Haptic Perception of Numerosity in Braille Characters with Changes in Scanning Velocity

Abstract

A single experiment involving braille was conducted to investigate the sensitivity of naïve readers of braille to differences in the numerosity of individual cells. The effect of scanning velocity on such perception was also measured. Twenty participants were asked to judge whether a particular braille cell had a different number of raised dots from others surrounding it. We used signal detection methodology to measure perceptual sensitivity and bias. Participants were asked to move a single finger along the lines of braille text at one of three constrained velocities (2-, 4-, or 8 cm/s). Instantaneous velocity and velocity intermittency during finger movements were computed using a digitizing tablet and a digitizing pen-tip. The data revealed that both numerosity difference manipulations (magnitude and direction) had significant effects on haptic sensitivity. Haptic detection ability was also influenced by constrained velocity. We consider the data in terms of both previous work on perceptual-motor control of braille reading and research on the mechanisms by which texture is perceived haptically.