The effect of masker interaural time delay on the masking level difference in children with history of normal hearing or history of otitis media with effusion.

OBJECTIVE

To determine the relation between the masking level difference (MLD) and the interaural time delay of the stimulus in children with a history of normal hearing and with a history of otitis media with effusion (OME).

DESIGN

MLDs for a 500 Hz pure tone presented in a 100 Hz-wide masking noise were determined as a function of the interaural delay of the masker (six interaural delays between -726 microsec and +998 microsec were examined). For the masker with zero interaural delay, the signal was presented either interaurally in-phase or 180 degrees out of phase. For the masker delay conditions, the signal was given the same interaural delay as the masker and then was inverted interaurally. All children had normal audiograms at the time of testing. Ten children had a history of normal hearing and seven children had a history of OME.

RESULTS

Similar to what has been found previously in adults, children with a history of normal hearing showed the maximum MLD (approximately 16 dB) for an interaural time delay of 0 microsec, with the MLD decreasing as a function of interaural time delay (by as much as 4 to 5 dB for the extreme delays). Children with a history of OME had significantly smaller MLDs than normal for the three smallest interaural delays but did not differ significantly from normal at the three largest interaural delays.

CONCLUSIONS

The form of the function relating masker interaural time delay to MLD magnitude is adult-like by age 6 yr. The function indicates a binaural advantage for the processing of sound near auditory midline. This advantage is less apparent in children having a history of OME.