Relating monaural and binaural measures of modulation sensitivity in listeners with and without hearing loss

Listeners are sensitive to interaural time differences carried in the envelope of high-frequency sounds (ITDENV), but the salience of this cue depends on certain properties of the envelope and, in particular, on the presence/depth of amplitude modulation (AM) in the envelope. This study tested the hypothesis that individuals with sensorineural hearing loss, who show enhanced sensitivity to AM under certain conditions, would also show superior ITDENV sensitivity under those conditions. The second hypothesis was that variations in ITDENV sensitivity across individuals can be related to variations in sensitivity to AM. To enable a direct comparison, a standard adaptive AM detection task was used along with a modified version of it designed to measure ITDENV sensitivity. The stimulus was a 4-kHz tone modulated at rates of 32, 64, or 128 Hz and presented at a 30 dB sensation level. Both tasks were attempted by 16 listeners with normal hearing and 16 listeners with hearing loss. Consistent with the hypotheses, AM and ITDENV thresholds were correlated and tended to be better in listeners with hearing loss. A control experiment emphasized that absolute level may be a consideration when interpreting the group effects.