Infants' ability to perceive the pitch of unresolved harmonics

An important phenomenon for models of pitch perception is that adult listeners can extract pitch from complexes containing only unresolved harmonics (UH). Although 3-month-olds discriminate resolved harmonics on the basis of missing fundamental (MF) pitch, their ability to discriminate UH is unknown. This study investigated the ability of adults, 7- and 3-month-olds to perceive the pitch of UH using an observer-based method. Stimuli were MF complexes that were bandpass filtered with a -12 dB/octave slope, combined in random phase, and presented at 70 dB SPL for 650 ms with a 50 ms rise/fall and a pink noise to mask distortion products. The experiment had two conditions: 1) "low" UH between 2500-4500 Hz based on MFs of 160 Hz (H17-H26) and 200 Hz (H13-H22) and 2) "high" UH between 4000-6000 Hz based on MFs of 190 Hz (H22-H31) and 200 Hz (H20-H29). To demonstrate MF pitch discrimination, participants were required to ignore spectral changes in complexes with the same fundamental and respond only when the fundamental changed. Interestingly, variable performance in the "high" condition was observed with adults. However, nearly all infants tested categorized complexes by MF pitch in both conditions, suggesting discrimination of unresolved harmonics at 3 months.