This experiment assessed 7-month-old infants' discrimination of harmon
ic complexes containing two, three, or five harmonics. In an operant h
ead-turn procedure, infants learned to discriminate between complexes
having fundamental frequencies of 160 Hz and 200 Hz. Infants were then
presented complexes that contained different-frequency harmonics and
were required to categorize them on the basis of their fundamental fre
quencies. Finally, the fundamental frequency was removed from the soun
ds, and infants were required to categorize them in accordance with th
e pitch corresponding to the missing fundamental. Although infants dis
criminated all the tonal complexes, they successfully categorized only
complexes containing three or five harmonics and failed to categorize
the two-harmonic complexes, even when they contained the fundamental
frequency. These results suggest that infants' perception of pitch det
eriorates as the number of harmonics in a tonal complex decreases. Fur
thermore, infants may need more spectral information to perceive pitch
than do adults, many of whom hear the pitch of the missing fundamenta
l for two-harmonic complexes.