Perceptual thresholds for single vs. Multi-Finger Haptic interaction

This paper presents experiments measuring psychophysical thresholds for multi-finger single point interaction with small haptic effects. Subjects used the UW Multi-Finger Haptic Display to interact with small haptic icons in a virtual environment. A forced-choice adaptive thresholding method is used to find a minimum detectable force magnitude. First, studies are performed to evaluate the consistency of our test apparatus across the four fingertips and to compare our application of the adaptive thresholding method to the prior work. Next, force detection thresholds for individual fingers are collected and compared to the force detection threshold using four fingers simultaneously. The results show comparable force detection levels between index, middle, pinkie and multi-finger interaction (33.5, 32.1, 33.5, 28.9 mN respectively) but less sensitivity with the ring finger (mean threshold of 43.6 mN). Repeated measures analysis of variance and t-tests with Bonferroni correction supports these conclusions. Most importantly, we show that the multi-finger threshold is not significantly lower than the threshold of the individual fingers. The implication for device design is that the relevant multi-finger device parameters are no more stringent than for single finger devices.