Abstract:
An experiment using lines of non-meaningful braille was designed to investigate the effects of numerosity difference and scanning velocity on haptic perception. Twenty-five participants were asked to determine whether a target braille cell had a different number of raised dots from others surrounding it. Three levels of numerosity difference and two levels of directional difference (the target had more or fewer raised dots than surrounding distractors) were manipulated. We hypothesised that participants who could self-select their speeds would show higher perceptual sensitivity than those who could not. Participants were required to scan lines at self-selected speeds during an initial session and consequently at either self-selected or constrained speeds during following sessions. Haptic perception to a target numerosity difference was measured using signal detection theory and a yes-no forced choice test. Instantaneous velocity and velocity intermittency during finger movements were also recorded using a digitizing tablet and a digitizing pen-tip. The experiment revealed that participants’ perceptual sensitivity increased with greater numerosity differences between the target cell and the distractor cells. This result suggests that braille cell numerosity may be processed and understood in terms of differences in dot density or texture. The direction of the difference was not significant. Participants who scanned lines of braille cells at a self-selected speed did not display greater sensitivity than those who scanned at constrained speeds. I also found that slower scanning speeds tended to produce higher discriminability, despite the fact that such slower movements are characterised by having highly fluctuating velocities, and faster movements, which are less intermittent, result in lower discriminability. Keywords: Braille, Numerosity, Haptic Perception, Reading Velocity