Influence of task-relevant and task-irrelevant feature continuity on selective auditory attention.

Past studies have explored the relative strengths of auditory features in a selective attention task by pitting features against one another and asking listeners to report the words perceived in a given sentence. While these studies show that the continuity of competing features affects streaming, they did not address whether the influence of specific features is modulated by volitionally directed attention. Here, we explored whether the continuity of a task-irrelevant feature affects the ability to selectively report one of two competing speech streams when attention is specifically directed to a different feature. Sequences of simultaneous pairs of spoken digits were presented in which exactly one digit of each pair matched a primer phrase in pitch and exactly one digit of each pair matched the primer location. Within a trial, location and pitch were randomly paired; they either were consistent with each other from digit to digit or were switched (e.g., the sequence from the primer's location changed pitch across digits). In otherwise identical blocks, listeners were instructed to report digits matching the primer either in location or in pitch. Listeners were told to ignore the irrelevant feature, if possible, in order to perform well. Listener responses depended on task instructions, proving that top-down attention alters how a subject performs the task. Performance improved when the separation of the target and masker in the task-relevant feature increased. Importantly, the values of the task-irrelevant feature also influenced performance in some cases. Specifically, when instructed to attend location, listeners performed worse as the separation between target and masker pitch increased, especially when the spatial separation between digits was small. These results indicate that task-relevant and task-irrelevant features are perceptually bound together: continuity of task-irrelevant features influences selective attention in an automatic, obligatory manner, consistent with the idea that auditory attention operates on objects.