A critical band filter in touch

Separate mechanoreceptor systems in humans were isolated by varying the spectra of vibrotactile stimuli. First, the function relating threshold to frequency of a sinusoid was obtained on the fingertip for each of four subjects, and it was found to comprise two limbs: a Pacinian and a non- Pacinian limb. The peak sensitivity within the Pacinian limb (mediated by Pacinian corpuscles) was around 250 Hz and spanned the region from 65 to 400 Hz. The non-Pacinian limb showed no detectable change in sensitivity in the region between 10 and 65 Hz. These two limbs were then treated as psychophysical channels in experiments in which narrow band noise and individual sinusoids were used to excite one or both channels. In the second and third experiments, the noise stimuli varied in bandwidth from 8 to 70 Hz and varied in center frequency from 25 to 218 Hz. Masking functions were obtained for ON-frequency conditions (the sinusoidal test and noise masker occupied the same frequency region) and for OFF-frequency conditions (the test and masker occupied different frequency regions). The ON-frequency experiments were used to estimate the signal-to-noise ratio (S/N) of the Pacinian channel at threshold. The OFF-frequency masking experiments were used to infer the shape of the Pacinian channel at frequencies below 65 Hz, where thresholds for Pacinian activation were above detection threshold. The results of these three experiments predicted the findings of a fourth masking experiment with a parameter free model that treated the Pacinian channel as a filter that integrates stimulus power. The results show that the Pacinian channel is analogous to a critical band in the auditory system.