Effects of listening task characteristics on auditory spatial attention in multi-source environment

Human listeners can readily extract sounds of interest from distracting sounds by directing their auditory spatial attention. Although the extent to which the auditory spatial attention influences listening performance and its spatial distribution in daily situations is important, the characteristics of this ability remain unclear. To investigate the characteristics of the auditory spatial attention, we measured the word intelligibility (4-mora words) and detection threshold of a target sound (1/12 octave-band noise burst) in the presence of distractor sounds (speech sounds/noises with the same bandwidth but with different center frequencies). In the experiment, we presented a target and multiple distractors simultaneously from loudspeakers surrounding the listeners. Results showed that word intelligibility improved when the target direction was attended compared to when it was not, whereas the detection threshold of the narrow-band noise was not influenced significantly by attention. These findings suggest that we can observe the effect of auditory selective attention when the listeners continuously direct their attention to a specific direction. Moreover, the spatial pattern of word intelligibility showed a peak corresponding to the attended direction. By contrast, the threshold of the narrow-band noise was constant regardless of the presented direction in which the target was presented.