Methods. (A) Tasks. Interaural time difference (ITD) discrimination (task A) and interaural level difference (ILD) discrimination (task B). On each trial, two pure tones of the same frequency were presented, one to each ear, over headphones, in each of two observation periods. The tones created a single intracranial sound image. Listeners selected the observation period in which the sound image was perceived to be farther to the right. The position of the sound image was manipulated by adjusting either the phase difference (ITD) or the level difference (ILD) between the tones presented to the two ears. (B) Regimens. Four groups of listeners were trained in a single session (day 1) on either task B (open rectangles) alone or on task A (filled rectangles) and task B in different regimens in which the primary manipulation was the number of consecutive training trials (60, 180, or 300) on each task. All listeners were then tested on task B the next day (day 2). (C) Learning measures. Learning on task B was assessed (1) between the mean threshold on day 1 and the mean threshold on day 2 (across-day learning; left), (2) between the thresholds on the last block on day 1 and the first block on day 2 (offline learning; middle), and (3) across the thresholds on each block on day 1 using the slope of the thresholds over the log transformed block number (within-session learning; right).
