Tonal Masking Level Difference in Children

The masking level difference (MLD) was investigated in 62 normal-hearing children, aged 7 to 13 years, who had no history of ear disease. The MLD is a psychoacoustic measure of binaural interaction and central auditory processing related to extracting signals from noise backgrounds. The MLD is a more efficient and less culturally biased predictive measure in the assessment of binaural interaction and auditory processing disorders compared to many linguistic or electrophysiologic techniques. In the first MLD condition, the masking noise was an interaurally in-phase (No) 160 Hz wide noise band centred on 500 Hz. The 500 Hz pure tone signal was generated digitally (rise-fall time, 100 msec, duration 2 sec), and presented either interaurally in-phase (So) or 180 degrees out-of-phase (S). In the second MLD condition, the 500 Hz pure tone signal was interaurally inphase (So) and the noise was either interaurally in-phase (No) or 180 degrees out-of-phase (N). The data were obtained using a simplified up-down adaptive procedure. Signals were presented using a GSI 16 audiometer with input from a digital audio system. The mean MLD was 11.21 dB (SD = 1.67) when the signal phase was changed and was 7.83 dB (SD = 1.75) when the noise phase was changed. Comparison is made between other studies that have measured the MLD. However, this would be the first such normative data obtained from Australian children and allows a comparative basis to other children, especially those with suspected binaural dysfunction.