Pitch perception: dissociating frequency from fundamental-frequency discrimination.

High-frequency pure tones (>6 kHz), which alone do not produce salient melodic pitch information, provide melodic pitch information when they form part of a harmonic complex tone with a lower fundamental frequency (F0). We explored this phenomenon in normal-hearing listeners by measuring F0 difference limens (F0DLs) for harmonic complex tones and pure-tone frequency difference limens (FDLs) for each of the tones within the harmonic complexes. Two spectral regions were tested. The low- and high-frequency band-pass regions comprised harmonics 6-11 of a 280- or 1,400-Hz F0, respectively; thus, for the high-frequency region, audible frequencies present were all above 7 kHz. Frequency discrimination of inharmonic log-spaced tone complexes was also tested in control conditions. All tones were presented in a background of noise to limit the detection of distortion products. As found in previous studies, F0DLs in the low region were typically no better than the FDL for each of the constituent pure tones. In contrast, F0DLs for the high-region complex were considerably better than the FDLs found for most of the constituent (high-frequency) pure tones. The data were compared with models of optimal spectral integration of information, to assess the relative influence of peripheral and more central noise in limiting performance. The results demonstrate a dissociation in the way pitch information is integrated at low and high frequencies and provide new challenges and constraints in the search for the underlying neural mechanisms of pitch.