Figure 1.

Stimuli and results from the main experiment. A, Stimuli. The low and high spectral regions consisted of harmonics 6–10 (Hn) of nominal F0s 0.28 and 1.4 kHz. The tones were presented either individually or all together as a harmonic tone complex. B, Mean F0DLs (left) and FDLs (right; ±SEM, n = 16). The numbers at the top represent the pure-tone frequencies (kHz) for the high-frequency and low-frequency regions. The filled circles represent predicted F0DLs based on optimal integration of the information from the individual harmonics, assuming a peripheral source of neural noise, before the integration of information (early-noise model). A qualitatively different pattern of integration is observed at the low and high frequencies, with poorer-than-optimal integration observed for low frequencies, and significantly better-than-optimal integration observed at high frequencies. The filled diamonds represent predicted F0DLs based on a more central source of neural noise, following the integration of information from the individual harmonics (late-noise model). The observed mean threshold is poorer than predicted in the low-frequency region, but not significantly different than that predicted in the high-frequency region. C, Ratio of predicted versus actual F0DLs for each participant, based on the early-noise model, with the mean for each frequency region shown by the colored bars. Individual ratios in the low-frequency region all fall below 1 and, except for one participant, ratios in the high-frequency region fall above 1.