Figure 2.

Psychophysical discrimination thresholds for binaural spatial cues. A, ILD thresholds across carrier frequency. Open squares, monkey Z; filled circles, monkey X; open diamonds, Macaca nemestrina (Houben and Gourevitch, 1979). Base SPL was 90 or 80 dB (monkey Z and X, respectively). B, Thresholds for IPD discrimination across carrier frequency in both monkeys; the dashed line traces comparable thresholds determined in humans by Klump and Eady (1965). The gray histogram shows distribution of best frequencies for all IPD-sensitive neurons (as determined by binaural beats, n = 268) on the same frequency axis. Thresholds are higher for carriers >1.5 kHz, the frequency range in which fewer neurons are sensitive to IPD. C, Same thresholds replotted as ITDs (in microseconds).