Two brief tones were presented in each observation period of a two-presentation, forced-choice trial. In the frequency-discrimination task (A), the two tones had a standard frequency (f) in one presentation and a lower comparison frequency in the other (f−Δf). In the interval-discrimination task (B), the two tones were separated by a standard interval (t) in one presentation and by a longer comparison interval in the other (t+Δt). The listener selected the comparison sound (lower frequency or longer interval). In most cases, during training the standard stimulus for both tasks had a frequency of 1 kHz and a temporal interval of 100 ms.

(A) Training regimens. Different groups of adults with normal hearing were given one of five daily training regimens for 6-11 days. In the three key regimens, in each session, practice on a target frequency-discrimination task (standard: 1 kHz, 100 ms) alternated with performance of either (1) a written symbol-to-number matching task in silence (Freq-alternating-with-Silence), (2) the written task while stimuli were played in the background (Freq-alternating-with-Sound), or (3) a temporal-interval discrimination task (Freq-alternating-with-Interval). The additional stimulus exposures (background sounds or stimuli for temporal-interval discrimination) had the same standard as in the target frequency-discrimination task, but varied in temporal interval rather than frequency. In the two remaining regimens all of the practice was on either the temporal-interval discrimination task (All-Interval (900 trials)) or the target frequency-discrimination task (All-Frequency (900 trials)), again with the 1-kHz, 100-ms standard. Each box represents 120 trials or the equivalent. (B) Pre- and post-training data. Mean frequency-discrimination thresholds (Δf in Hz for 79.4% correct) before (open squares) and after (filled squares) completing one of the five multiple-day training regimens (n=6-8 per trained group) or receiving no training over that same time period (controls; n=10). Results are shown for the standard stimulus used in all of the training regimens (top: 1 kHz, 100 ms) and for the two untrained standard stimuli used to test the generalization of learning (middle: 1 kHz, 50 ms and bottom: 4 kHz, 100 ms). Error bars indicate +/− one standard error of the mean. Dashed boxes indicate significantly greater improvement between the pre- and post-training tests by a trained group than controls (p< 0.05). (C) Performance across sessions. Group mean thresholds (squares) across sessions for the target frequency-discrimination task (standard: 1 kHz, 100 ms) for each of the four groups who practiced frequency discrimination (panels), with regression lines fitted to the thresholds on the log of the session number. Error bars indicate +/− one standard error of the mean. Thresholds were adjusted to account for individual differences in pre-training threshold (Equation in Cohen, 1988). The p-values reflect whether the slope of the regression line was significantly different from zero. The key result is that the combination of practice on the target frequency-discrimination task and additional stimulus exposures (Freq-alternating-with-Sound and Freq-alternating-with-Interval) facilitated learning on frequency discrimination. Learning was enhanced relative to when the training involved only the target-task performance portion of the combined regimens (Freq-alternating-with-Silence), as well as to when stimulus exposures in greater numbers than in those regimens were presented in the absence of target-task performance (All-Interval (900 trials)).

(A) Training regimens. In one regimen all of the practice in each session was on a target frequency-discrimination task (standard: 1 kHz, 100 ms) (All-Frequency (360 trials)). In the other three regimens, in each session, practice on the target frequency-discrimination task occurred either (1) exclusively before performance of a temporal-interval discrimination task (Freq-then-Interval), (2) exclusively after performance of that temporal-interval task (Interval-then-Freq), or (3) exclusively after performance of a written symbol-to-number matching task while stimuli were played in the background (Sound-then-Freq). Otherwise, as in Fig. 2. (B) Pre- and post-training data. As in Figure 2, with the data from controls (see Fig. 2) replotted for comparison. (C) Performance across sessions. As in Figure 2. The key result here is that the additional stimulus exposures enhanced learning on the target frequency-discrimination task regardless of whether those exposures were presented exclusively before or after target-task performance.

(A) Training regimens. In one regimen all of the practice in each session was on a target frequency-discrimination task (standard: 1 kHz, 100 ms) (All-Frequency (360 trials)). In the other three regimens, in each session, practice on the target frequency-discrimination task occurred prior to performance of a temporal-interval discrimination task using the same standard stimulus, with the two events separated by either (1) 0 minutes (Freq-then-Interval), (2) 15 minutes (Freq-15 min-Interval), or (3) 4 hours (Freq-4 hour-Interval). Otherwise, as in Fig. 2. (B) Pre- and post-training data. and (C) Performance across sessions. As in Figure 2, with the data from controls (see Fig. 2) and from the All-Frequency (360 trials) and Freq-then-Interval groups (see Fig. 3) replotted for comparison. The key result here is that some benefit from the additional stimulus exposures remained when they were presented 15 minutes, but not 4 hours, after performance of the target frequency-discrimination task.

(A) Training regimens. In one regimen all of the practice in each session was on a target frequency-discrimination task (standard: 1 kHz, 100 ms) (All-Frequency (360 trials)). In the other three regimens, in each session, practice on the target frequency-discrimination task immediately preceded performance of a temporal-interval discrimination task. As compared to the standard stimulus used in the target frequency-discrimination task, the standard for the temporal-interval discrimination task either (1) was the same (1 kHz, 100 ms; Freq-then-Interval), (2) had a different frequency but the same temporal interval (4 kHz, 100 ms; Freq-then-Interval (different frequencies)), or (3) had the same frequency but a different temporal interval (1 kHz, 50 ms; Freq-then-Interval (different intervals)). Otherwise, as in Fig. 2. (B) Pre- and post-training data. and (C) Performance across sessions. As in Figure 2, with the data from controls (see Fig. 2) and from the All-Frequency (360 trials) and Freq-then-Interval groups (see Fig. 3) replotted for comparison. The key result here is that the additional stimulus exposures led to enhanced learning on the target frequency-discrimination task only when those exposures had the same frequency as, though they did not have to be identical to, the stimuli encountered during performance of the target task.