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

Abstract

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.

FIG. 1

A The four location–pitch conditions. Time is represented as distance from the head so that the primer phrase (P) comes first, followed by the two concurrent digit pairs (three and four form the first pair and five and two form the second). Pitch is denoted by font weight, with boldface type representing the primer pitch and light type representing the alternate pitch. B The method of stimulus generation. Each row is a processing channel that is comb filtered and convolved with an HRIR at a certain azimuth. Pitch is denoted by font weight as above. In this example, the correct response when attending location would be [3, 5], and when attending pitch would be [4, 5].

FIG. 2

Summary response data collapsed across angle and pitch separation when attending location (A) and pitch (B). Each column is one of the four possible conditions (in the same order as they appear in Fig. 1A), and each color-coded portion of the bar corresponds to a specific response type. There were four response types: correct, in which both digits were correctly reported; wrong-feature, in which the subject reported the digits that would have been correct under the alternate attention instructions; confusion, which is any error that is not a wrong-feature error, but no digits which were not present in the stimulus were reported; and guessing, in which the subject reported at least one number that was not present in the stimulus.

FIG. 3

The effect of directing attention in the consistent condition. There was a higher percentage of correct responses when attending location (solid lines, triangular markers) than when attending pitch (dashed lines, circular markers), despite the fact that for both sets of instructions, both location and pitch could have helped reinforce the correct digits. The x-axes of the upper panel (A) represent angle separation, with each of the three plots corresponding to one of three pitch separations, increasing from left to right. The lower three plots (B) show the same data with the x-axes now representing pitch separation and each of the three plots corresponding to one of the three location separations. Correct responses in the attend-location blocks increased with spatial separation, but were unaffected by pitch separation. In the attend-pitch trials, the percentage of correct responses increased with both the task-relevant feature and the task-irrelevant feature. Error bars represent ±1 SEM.

FIG. 4

The effect of directing attention in the opposing condition. A The percentage of trials for each configuration in which the listeners based their responses on location. As in Figure 3, trials from attend-location blocks are shown as solid lines with triangular markers, and trials from attend-pitch blocks are shown as dashed lines with circular markers. Using the same color codes from Figures 2 and 3, the correct responses (answered based on location in an attend-location block) are shown in black and wrong-feature responses (answered based on location in an attend-pitch block) are shown in light gray. Angle separation is on the x-axis and each of the three plots in the row corresponds to one of the three pitch separations, increasing from left to right. B The same as (A), but for responses based on pitch. Accordingly, the x-axes now represent separation with each of the three plots corresponding to an angle separation. The line styles to indicate attend-pitch and attend-location trials are the same; however, the colors have been reversed to indicate that responding based on pitch is correct (black) in attend-pitch trials, and constitutes a wrong-feature response (light gray) in attend-location trials. Error bars are ±1 SEM; where not visible, they are small enough to be hidden by the markers.