Figure 1.
Example tuning curves, responses, and spike-count covariance matrix for the virtual cortical population.
A. Example neural tuning curves for neurons with different BFs in primary auditory cortex. B. Example population response. The stimulus was a pure tone with a frequency of 1000: mean spike rates as a function of BF. Circles: simulated spike counts. C. Spike-rate covariance matrix. Entries on the diagonal correspond to spike-count variances for individual units and are equal to the spike rates shown in panel B. Off-diagonal entries correspond to covariances between the spike counts of different units, and are equal to the geometric mean of the units' spike rates times the spike-count correlation coefficient. D. Correlation matrix corresponding to the covariance matrix shown in panel C. See Methods for details.
Figure 2.
Population responses evoked by tones differing in frequency or intensity.
A. Population responses evoked by two tones differing slightly in frequency. Blue: mean spike rate as function of BF for a 1000 Hz, 50 dB SPL pure tone. Red: mean spike rate as function of BF for a 1001.68 Hz, 50 dB SPL pure tone. B. Spike-rate difference (Δr) and d′/unit as a function of BF. The spike-rate difference was obtained by subtracting the mean spike rate evoked by the higher-frequency stimulus (red curve in panel A) from the spike rate evoked by the lower-frequency stimulus (blue curve). d′/unit was computed as described in Experimental Procedures. C. Population responses evoked by two tones differing slightly in intensity. Blue: mean spike rate as function of BF for a 1000 Hz, 50 dB SPL pure tone. Red: mean spike rate as function of BF for 1000 Hz, 51.22 dB SPL pure tone. D. As for panel B, but for the population responses shown in panel C.
Figure 3.
Schematic illustration of the impact of correlations on spike-rate distributions for frequency and intensity discrimination.
A. Horizontal slices across spike-rate distributions evoked by two stimuli differing in frequency in two units with BFs below and above the reference-stimulus frequency. The spike rate of the unit (i) with BF lower than the reference frequency is plotted along the x-axis; the spike rate of the unit (j) with BF higher than the reference frequency is plotted along the y-axis. Blue: horizontal slice across the spike-rate distribution for the reference tone (1000 Hz, 50 dB SPL); red: horizontal slice across the spike-rate distribution for the higher-frequency tone. B. Same as A, but for an intensity change.