Stimulus amplitude versus firing rates.

<p>(A) Mean rate-intensity function for neurons in area 3b, computed from responses to sinusoids; marker colors change from dark to bright red with increasing stimulation frequency; error bars denote standard error of the mean. The shallow and frequency-independent increase in firing rate at low amplitudes is due to progressive neuronal recruitment and is not observed in the responses of individual neurons (see <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001558#pbio.1001558.s001" target="_blank">Figure S1A</a>). (B) Rate-intensity function for neurons in area 3b, computed from responses to band-pass noise stimuli; colors change from dark to bright red as the center frequency of the noise increases; markers denote different noise conditions (triangle, noise_A; circle, noise_V; square, noise_P, see <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001558#s4" target="_blank">Materials and Methods</a>). For both individual neurons and neural populations, responses are independent of the frequency composition of the stimulus. (C) Hilbert transform of a sample noise stimulus (black) and smoothed time-varying population firing rates (gray) in areas 3b (top), 1 (middle), and 2 (bottom). The neural response is time-shifted to account for neural delays. (D) Mean correlation between the time-varying population response and the logarithm of the stimulus envelope in the three areas.