Background/Purpose Previous research has shown that exposure to short-term hand and arm vibration degrades several aspects of motor performance (Fischman & Lehman, 2004; Gerard & Martin, 1999; Martin et al., 1991). However, vibration may be useful for helping blind individuals use the internet. We are developing a prototype board that maps low levels of vibration to locations on a computer monitor. The initial goal of the current project was to determine the just noticeable difference in levels of finger vibration that can be correctly detected by an individual.
Method Thirty-three sighted subjects placed their preferred index finger on an accelerometer mounted on a vibratory shaker that vibrated at frequencies from 50 – 130 Hz in 20-Hz increments. All possible pairwise combinations were presented, and subjects made a “same” or “different” discrimination to each pair. On 25 trials subjects were able to hear the sound of the shaker (“Sound”), and 25 trials were performed with headphones (“No-Sound”).
Analysis/Results Overall, the percentage of incorrect discriminations was 15.4% for “Sound” and 16.4% for “No-Sound.” This difference was not statistically significant, p > .05, indicating that hearing the vibration provided no advantage. Only four pairings produced 100% correct discriminations, and these differed by at least 60-Hz. The most difficult discrimination (74% error rate) was the pairing of 90-Hz followed by 70-Hz. However, when 70-Hz preceded 90-Hz, the error rate was only 32%.
Conclusions Sighted humans can accurately discriminate levels of finger vibration in the range tested when the pairings differ by at least 40-Hz.