Infants require low-frequency energy to hear the pitch of the missing fundamental.

The present experiment assessed 7- to 8-month-old infants' perception of pitch for harmonic tonal complexes containing either low- or high-frequency energy. In a visually reinforced, operant head turn procedure, infants first learned to discriminate two harmonic tonal complexes based on missing fundamental frequencies of 160 and 200 Hz. After learning this basic task, infants were presented with spectrally varying harmonic tonal complexes that contained either resolvable, low-frequency energy, or unresolvable, high-frequency energy. Infants learned to categorize the low-frequency signals according to the pitches of their missing fundamental frequencies but failed to categorize the high-frequency signals. These results suggest that infants require low-frequency, resolvable energy to hear the pitch of the missing fundamental.