Effects of steady background noise on binaural pitch fusion

Abstract

Binaural pitch fusion is the fusion of dichotic stimuli across the two ears. The current study was designed to investigate how steady background noise can influence binaural fusion. The binaural fusion ranges, the frequency ranges over which binaural fusion occurred, were measured with various levels (30—70 dB/ERBN) of the threshold-equalizing noise (Moore et al., 2004) and compared with those measured in quiet. Two interleaved adaptive procedures were used to estimate the fusion ranges at the reference frequencies of 2 and 3 kHz: Single-Interval Adjustment Matrix (SIAM; Kaernbach, 1990) and Maximum-Likelihood (ML; Green, 1992). The results show that the TEN decreases the fusion ranges to about 1.5 to 2 times narrower than those in the quiet condition. Even soft noise levels (i.e., the 30 dB/ERBN) significantly decreased fusion ranges. For some subjects, the fusion range asymptoted with a soft level and did not increase with increased noise level; for other subjects, the fusion range minimized only at the specific noise level. Both SIAM and ML procedures showed similar performance in fusion range estimation. The findings suggest that the importance of steady background noise, specifically TEN, in binaural fusion may vary across subjects. This may provide potential rehabilitation approaches to reduce broad fusion in hearing impaired listeners.Binaural pitch fusion is the fusion of dichotic stimuli across the two ears. The current study was designed to investigate how steady background noise can influence binaural fusion. The binaural fusion ranges, the frequency ranges over which binaural fusion occurred, were measured with various levels (30—70 dB/ERBN) of the threshold-equalizing noise (Moore et al., 2004) and compared with those measured in quiet. Two interleaved adaptive procedures were used to estimate the fusion ranges at the reference frequencies of 2 and 3 kHz: Single-Interval Adjustment Matrix (SIAM; Kaernbach, 1990) and Maximum-Likelihood (ML; Green, 1992). The results show that the TEN decreases the fusion ranges to about 1.5 to 2 times narrower than those in the quiet condition. Even soft noise levels (i.e., the 30 dB/ERBN) significantly decreased fusion ranges. For some subjects, the fusion range asymptoted with a soft level and did not increase with increased noise level; for other subjects, the fusion range minimized only at the...