Diotic and dichotic perception of single echoes

The perception of single echoes for two binaural listening modes, diotic and dichotic was examined. Stimuli consisted of a white Gaussian noise waveform added to itself with an intervening delay. Delay values of 2, 4, 8, and 16 ms at two overall sensation levels of 30 and 50 dB SL were used. The dichotic listening mode was created by reversing the polarity of the delayed noise waveform in one ear relative to the other ear. An ABX paradigm was used to determine the absolute threshold for the presence of a single echo. Diotic listening mode thresholds were found to be significantly different from dichotic listening mode thresholds. For delay values of 2 and 4 ms, the diotic listening mode thresholds were substantially elevated relative to the dichotic listening mode thresholds. Diotic threshold data appear to be compatible with existing critical-band models. Dichotic threshold results lend support to a mechanism of binaural combination which serves to reduce spectral variation.