Experimental design. A, Trial structure for the auditory selective attention task. For attend-left and attend-right trials, an auditory cue was presented via headphones with the same interaural time difference (ITD) as the target melody. For passive trials, a diamond appeared around a central fixation dot on screen. During the stimulus period, subjects kept their gaze on the fixation dot, while melodies were presented diotically. A green circle appeared around the fixation dot to prompt a response. Subjects were to press 1, 2, or 3 on the keyboard to indicate if the melody was “rising,” “falling,” or “zigzagging,” respectively. Visual feedback was given after button press to indicate if the target was correctly identified; for passive trials, no button press was considered a correct response. B, Left (blue), right (red), and center (gray) melodies were composed of notes with different fundamental frequencies (F0). Note that in this example, right melodies had the highest fundamentals while left melodies had the lowest fundamentals, but the opposite also occurred with equal probability. The center melody always had the same F0s, which were between F0s of the left and right melodies. Individual melodies also changed pitch over time, such that they were rising, falling, or zigzagging, illustrated by blue, red, and gray bars in this example, respectively.