Effect of Rate of Change of Stimulus

TLDR: It has been shown that the assumption of a fixed Weber fraction for a user is not correct and it is a monotonic function of the temporal variation of the stimulus.

Abstract: In the literature, it has been assumed that the Weber fraction is always fixed for an individual and is independent of any temporal variation in the stimulus. If the assumption is not correct, the perceptual limitations of a human being are not fully exploited by the fixed Weber fraction. For example, if the signal changes very slowly, it is difficult for a user to react to the change, and when the change is too quick, the user may not be able to respond because of nonzero human response time (minimum time required for reacting to a change). Thus, a fixed Weber fraction will contribute inessential data packets for such kind of signals. This leads us to examine how the perceptual deadzone is affected by the rate of change in the kinesthetic force stimulus. In this chapter, we take up this particular study. For this purpose, we design an experiment where a user is exposed to either a linearly increasing (positive slope) or decreasing (negative slope) haptic force stimulus with a varying slope S, and is asked to react to the change. We intend to find a decision boundary as a function of the rate of change of stimulus (slope) to compute the Weber fraction. We apply both parametric and nonparametric classifiers on the recorded data to estimate the best-fit decision boundary. We demonstrate that the Weber fraction decreases monotonically with an increase in the slope for both positive and negative regions. It means that as the slope is increased, the change in the signal is more easily perceivable. We also demonstrate that there is an asymmetric behavior of perception between the increasing and the decreasing force stimuli. Hence, it has been shown that the assumption of a fixed Weber fraction for a user is not correct and it is a monotonic function of the temporal variation of the stimulus.