Contralateral masking effects in dichotic listening with two competing talkers in the target ear

Some of the most influential experiments in selective auditory attention have been based on a dichotic cocktail party task where listeners are asked to respond to a speech signal presented to one ear while ignoring a simultaneous competing speech signal presented to the other ear. These experiments have generally shown that the intelligibility of a monaural speech signal is unimpeded by the presence of an interfering speech signal at the opposite ear. However, recent results in our laboratory indicate that listeners cannot ignore a speech signal at the unattended ear when two simultaneous speech signals are presented to the target ear. In this study, the intelligibility of a target phrase in a two-talker stimulus presented to one ear was measured monaurally and with a speech or noise signal in the opposite ear. Performance in this task was unaffected when noise was added to the unattended ear, but degraded substantially when speech was added to the unattended ear. These results suggest that there are strong interactions between the monaural processes that listeners use to segregate two spatially colocated voices and the binaural processes they use to segregate voices originating from different apparent locations in space. [Work supported by AFOSR.]