FIG. 5.

Firing rates as a function of vibratory frequency for SA1 (left) and RA fibers. Each trace corresponds to a spatial period. The amplitudes were chosen such that the stimuli were equated in subjective intensity, as measured in a companion psychophysical study (Bensmaia et al. 2005). Firing rates evoked by gratings vibrating at 40 Hz were depressed for both SA1 and RA fibers. The specific reason for the drop in spike rate at 40 Hz is unclear. However, the decline is likely due to the way in which signals from the relevant populations of mechanoreceptive afferent fibers are combined to convey information about the subjective magnitude of the stimulus. When stimuli were set relative to the sensitivity of individual fibers, the neural response was no longer anomalous at 40 Hz.