Rate dependency of vibrotactile stimulus modulation.

Adaptation has a pronounced impact on the perception of vibrotactile stimuli. Previously, we demonstrated that the duration of vibrotactile conditioning was directly proportional to the impact that adaptation has on sensory perception (Tannan et al., 2007b). Prior reports had proposed that the impact of adaptation on the perceived magnitude of vibrotactile stimuli was specific to the conditioning amplitude (Goble and Hollins, 1993), and this concept led us to hypothesize that if the amplitude of a vibrotactile stimulus was changed continuously, that this modulation would itself impact adaptation. In order to test this idea, two repetitive vibrotactile stimuli were simultaneously delivered to two adjacent finger tips (D2 and D3). In a matching task, a standard stimulus was maintained at constant amplitude (defined as "stationary"), while the amplitude of the test stimuli was increased at a fixed rate (i.e., 10 μm/s; defined as "non-stationary") from a null value up to the level that a subject (n=50) indicated that the two stimuli were perceived to be identical. Changing the standard amplitude yielded results consistent with Weber's Law and changing the modulation rate yielded results that were consistent with our initial hypothesis that faster modulation rates would lead to the non-stationary stimulus as being less adapted. A comparative study, using the above-described method, was conducted with 12 autism subjects who were previously reported to have below normal adaptation metrics (Tannan et al., 2008). The findings of this pilot autism study suggest that rate dependent modulation of vibrotactile stimuli could provide a more sensitive metric of adaptation, as the observations demonstrate a bimodal distribution within the autism spectrum.