Journal of Neuroscience, Vol 15, 2808-2818, Copyright © 1995 by Society for Neuroscience
A critical band filter in touch
JC Makous, RM Friedman and CJ Vierck Jr
Department of Neuroscience, University of Florida, Gainesville 32610- 0244, USA.
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.