Nonspatial Features Reduce the Reliance on Sustained Spatial Auditory Attention.

OBJECTIVE

Top-down spatial attention is effective at selecting a target sound from a mixture. However, nonspatial features often distinguish sources in addition to location. This study explores whether redundant nonspatial features are used to maintain selective auditory attention for a spatially defined target.

DESIGN

We recorded electroencephalography while subjects focused attention on one of three simultaneous melodies. In one experiment, subjects (n = 17) were given an auditory cue indicating both the location and pitch of the target melody. In a second experiment (n = 17 subjects), the cue only indicated target location, and we compared two conditions: one in which the pitch separation of competing melodies was large, and one in which this separation was small.

RESULTS

In both experiments, responses evoked by onsets of events in sound streams were modulated by attention, and we found no significant difference in this modulation between small and large pitch separation conditions. Therefore, the evoked response reflected that target stimuli were the focus of attention, and distractors were suppressed successfully for all experimental conditions. In all cases, parietal alpha was lateralized following the cue, but before melody onset, indicating that subjects initially focused attention in space. During the stimulus presentation, this lateralization disappeared when pitch cues were strong but remained significant when pitch cues were weak, suggesting that strong pitch cues reduced reliance on sustained spatial attention.

CONCLUSIONS

These results demonstrate that once a well-defined target stream at a known location is selected, top-down spatial attention plays a weak role in filtering out a segregated competing stream.