Infants' sensitivity to broadband noise.

Infants have higher pure-tone thresholds than adults. One explanation is that infants do not adopt the frequency-selective listening strategy that adults use when detecting tones. In contrast to other models of infants' immature sensitivity, the listening strategy account predicts that infants will be more sensitive to broadband sounds, relative to adults. Infants 7-9 months old were tested in two experiments to examine their sensitivity to broadband noise. Unmasked and masked thresholds for a 1000-Hz tone and for broadband noise were estimated adaptively for infants and adults using an observer-based behavioral procedure. The difference between infants and adults in unmasked threshold were 14 and 7 dB for tones and noise, respectively. The difference between infants and adults in masked threshold were 10 and 5 dB for tones and noise, respectively. Psychometric functions for detection of broadband noise were also obtained from some infants and adults. Infants' psychometric functions were similar to those obtained in tone detection with shallower slopes and lower upper asymptotes than adults'. This suggests that the relative improvement in infants' threshold for broadband noise is not due to greater attentiveness to the noise. A model of infants' sound detection invoking inattentiveness, listening strategy, and an unspecified source of internal noise may account for the characteristics of the infant psychometric function.