A critical band filter in touch

Abstract

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.

Texture perception through direct and indirect touch: An analysis of perceptual space for tactile textures in two modes of exploration

“…One quantity that influences perceived roughness through indirect touch is vibratory power: as the probe is scanned across a textured surface, the probe interacts with the surface in such a way as to produce vibrations. One difference between the power measure used by Bensmaia and Hollins and the one adopted here is that their vibrations were filtered using the inverted Pacinian threshold power as a function of frequency (following Makous et al 1995). In the present study, raw power was as good a predictor of perceived roughness as was Pacinian-filtered power (the correlation between roughness and power was 0.92 for raw power and 0.89 for PC-weighted power).…”

Vibrotactile intensity and frequency information in the Pacinian system: A psychophysical model

“…Diharmonic stimuli were adjusted so that (1) the two frequency components of each stimulus were of equal amplitude and (2) the overall Pacinian-weighted power of each stimulus was equal to that of simple sinusoids at each of the three chosen sensation levels. Following Makous et al (1995), the ability of each spectral component to excite the Pacinian system was expressed as a function of its spectral power (A 2 f 2 ) divided by threshold power (T 2 f 2 ) at that frequency. According to Makous et al, this quantity, summed across all frequencies, constitutes a measure of the ability of a stimulus to excite the Pacinian system.…”

“…The objective was to infer, from the pattern of confusions, the degree to which the Pacinian system could convey temporal and intensive information about the stimuli. We wished to ascertain whether the discriminability of a pair of stimuli could be fully explained in terms of the intensity of these stimuli, as previous findings might suggest (Makous, Friedman, & Vierck, 1995), or whether temporal factors also play a role in shaping the vibratory percept. We first impleThis work was supported by the Cognitive Science Program of the University of North Carolina at Chapel Hill.…”

“…The Pacinian system has been likened to a critical band filter, drawing an analogy with the auditory system (Makous et al, 1995;Marks, 1979). This analogy is apt, given the similarity of the relevant energies in the two sensory modalities.…”

Some characteristics of tactile channels

“…rived from these forward masking tuning curves is that at lower frequencies the sensitivity of the P channel becomes much less affected by changes in frequency. Makous, Friedman and Vierck [16] also derived tuning curves for the P channel that flatten out at low frequencies.…”