Figure 1. Response profile for a single unit in the primary auditory cortex. A, frequency/intensity response area determined with tones presented binaurally with 0 μs ITD. The maximum tone level is 100 dB SPL (±5 dB) across this range. Vertical white line indicates the frequency (500 Hz) of the tone used subsequently. Horizontal line indicates the level of the noise entering the same auditory filter as the signal. B, Rate-level functions for broadband noise presented to the left ear (blue thin line), right ear (red dashed line), or both ears simultaneously (black thick line) at varying sound levels. Vertical line indicates the constant noise spectrum level of 23 dB SPL used for noise-delay and MRLFs. C, Tone delay function for a 500 Hz tone presented at 50 dB SPL. Red vertical line indicates best ITD. D, Noise delay function for broadband noise presented at 23 dB SPL spectrum level. Red curve indicates smoothed noise delay function. Red vertical line indicates best ITD. E, F, MRLFs for N0S0 (E, filled squares), N0Sπ (E, open squares), NπSπ (F, filled circles), and NπS0 (F, open circles). Small red symbols represent the corresponding SDs. In each case, a 500 Hz tone was presented at varying signal levels against a broadband background noise set at a constant level of 23 dB SPL spectrum level. G, Variance of spikes/stimulus versus mean spikes/stimulus pooled across all conditions shown in E and F. Diagonal black line indicates equality. Red line indicates the fitted slope. H, PSTHs with 1 ms resolution pooled across all conditions plotted in E (left) and F (right). Red vertical lines indicate the spike counting window. I, Raster plots for the conditions shown in E and F. Fifty repeats at each signal level are distributed vertically for each sound level increasing vertically. Red vertical lines indicate the spike counting window.