Masking-Level Differences in the Elderly

A Comparison of Antiphasic and Time-Delay Dichotic Conditions

Four dichotic thresholds (SN₀, S₀N, S_0;N, and SN,) were measured for young and old subjects using both burst and continuous broadband maskers. Masking-level differences (MLDs) were determined by subtracting dichotic thresholds from homophasic thresholds (S₀N₀ or SN). The S₀N thresholds for the old subjects did not differ significantly from those for the young subjects in either the continuous or the burst masking noise conditions. The SN thresholds for the old subjects did not differ significantly from those for the young subjects in the continuous masking noise condition, but there was a significant age effect (3 dB) when burst masking noise was used. Both young and old subjects obtained larger MLDs in continuous masking noise than in burst masking noise. MLDs for old subjects were smaller than MLDs for young subjects by 4.3, 5.0, 2.7, and 1.6 dB in burst masking noise and by 4.9, 3.5, 2.5, and 1.4 dB in continuous masking noise, respectively in the SN₀, SN, S₀N, and S₀N conditions. For young subjects there was a hierarchy n the size of the MLD obtained in the four dichotic conditions, with the MLD being significantly larger in the SN₀ and S₀N, conditions; however, the size of the MLD was the same in all four conditions for the old subjects. Compared to young subjects, the performance of the old subjects was characterized by decreased ability to use homophasic cues In burst masking noise and decreased ability to use interaural difference cues. These findings were observed at four signal frequencies.

KEY WORDS: binaural processing, masking-level difference, interaural time-delay, masked thresholds, elderly

Submitted on July 31, 1990
Accepted on January 3, 1991

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