Enhancing perceptual learning by combining practice with periods of additional sensory stimulation

Abstract

Perceptual skills can be improved even in adulthood, but this learning seldom occurs by stimulus exposure alone. Instead, it requires considerable practice performing a perceptual task with relevant stimuli. It is thought that task performance permits the stimuli to drive learning. A corresponding assumption is that the same stimuli do not contribute to improvement when encountered separately from relevant task performance because of the absence of this permissive signal. However, these ideas are based on only two types of studies, in which the task was either always performed or not performed at all. Here we demonstrate enhanced perceptual learning on an auditory frequency-discrimination task in human listeners when practice on that target task was combined with additional stimulation. Learning was enhanced regardless of whether the periods of additional stimulation were interleaved with or provided exclusively before or after target-task performance, and even though that stimulation occurred during the performance of an irrelevant (auditory or written) task. The additional exposures were only beneficial when they shared the same frequency with, though they did not need to be identical to, those used during target-task performance. Their effectiveness also was diminished when they were presented 15 min after practice on the target task and was eliminated when that separation was increased to 4 h. These data show that exposure to an acoustic stimulus can facilitate learning when encountered outside of the time of practice on a perceptual task. By properly using additional stimulation one may markedly improve the efficiency of perceptual training regimens.

Figures

Figure 1.

The frequency- and temporal-interval discrimination tasks. 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.

Figure 2.

Initial experiments. A, Training regimens. Different groups of adults with normal hearing were given one of five daily training regimens for 6–11 d. 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-Freq (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 ±SEM. 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 ±SEM. Thresholds were adjusted to account for individual differences in pretraining threshold (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)].

Figure 3.

Follow-up experiments: presentation order. 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-Freq (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 Figure 2. B, Pre- and post-training data. As in Figure 2, with the data from controls (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.

Figure 4.

Follow-up experiments: temporal separation. 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-Freq (360 trials)]. In the other three regimens, in each session, practice on the target frequency-discrimination task occurred before performance of a temporal-interval discrimination task using the same standard stimulus, with the two events separated by either (1) 0 min (Freq-then-Interval), (2) 15 min (Freq-15 min-Interval), or (3) 4 h (Freq-4 h-Interval). Otherwise, as in Figure 2. B, C, Pre- and post-training data (B) and performance across sessions (C). As in Figure 2, with the data from controls (Fig. 2) and from the All-Freq (360 trials) and Freq-then-Interval groups (Fig. 3) replotted for comparison. The key result here is that some benefit from the additional stimulus exposures remained when they were presented 15 min, but not 4 h, after performance of the target frequency-discrimination task.

Figure 5.

Follow-up experiments: stimulus dependence. 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-Freq (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 with 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 Figure 2. B, C, Pre- and post-training data (B) and Performance across sessions (C). As in Figure 2, with the data from controls (Fig. 2) and from the All-Freq (360 trials) and Freq-then-Interval groups (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.