The masking-level difference in children.

The masking-level difference (MLD) was investigated in children aged 3.9 to 9.5 years and in an adult control group in order to examine the development of the MLD with age. A three-alternative forced-choice adaptive tracking procedure was used for all listeners. MLDs were determined for a 500-Hz pure-tone signal presented in a 300-Hz-wide masking noise centered on 500 Hz, where both interaural time and amplitude cues were present, and in 40-Hz-wide maskers centered on 500 Hz, where either amplitude (MLD delta a) or time (MLD delta t) cues were present. The masking noise level was fixed at 60 dB/Hz SPL. For the 300-Hz-wide masker, the MLDs of the children increased in magnitude up until the age of 5 or 6 years. For the 40-Hz-wide maskers, the MLDs of the 5- and 6-year-old children were still somewhat below adult values. It is possible that these differences between adults and children are related to the development of the peripheral/brainstem auditory system. By this interpretation, the MLD might be small in young listeners because the interaural time and amplitude cues underlying the MLD are coded with relatively poor precision. However, it is perhaps more likely that these differences are coded precisely in the peripheral auditory system, but that more central auditory processes are relatively inefficient in extracting the interaural information.