Effect of extrinsic noise on vibrotactile information processing channels

Cutaneous receptors sensitive to high-frequency vibration produce spatial summation at threshold levels of stimulation, whereas the response of the receptor population sensitive to low frequencies appears to be independent of contactor size at threshold. Reports have been made of a phenomenon in which the presumably nonsummating population of mechanoreceptors produce spatial summation at suprathreshold levels. A possible explanation concerns the relative signal-to-noise ratios of cutaneous mechanoreceptor systems. By selectively masking the systems with narrow-band and wide-band noise, it can be shown that any combination of signal frequency, masking noise, and contactor size that predominantly activates either system results in a linear effect of the masker on the threshold of the signal. Combinations of the experimental variables that activate both receptor systems simultaneously reduce the effect of the masking by one-half. This is interpreted as evidence of an interactive process between receptor systems within the central nervous system. The effects of signal-to-noise ratio and intrasensory interactions are discussed.