Learning two things at once: differential constraints on the acquisition and consolidation of perceptual learning

Abstract

Learning is often prevented by events that occur after training, an outcome that is usually attributed to the disruption of consolidation-the transfer of learning to long-term memory. Here, we provide evidence from perceptual learning that improvements in performance can also be blocked by intervening events that occur during the acquisition phase of learning-the period of active practice. Listeners improved on each of two conditions of auditory temporal-interval discrimination (100 and 350 ms) when the two were practiced consecutively, even though that is a classic disruption-of-consolidation regimen. However, when practice on these two conditions was interleaved, there was no learning on either condition. The failure to improve in the interleaved case indicates that, at least in some circumstances, learning can be prevented during acquisition by events that do not disrupt consolidation itself. These results thus suggest that acquisition and consolidation are distinct phases in human learning.

Figure 1. Average group discrimination thresholds on the pre- (empty symbols) and post- (filled symbols) test sessions for the control, interleaved, and consecutive groups

Results are shown for the two trained conditions (first row), and for untrained conditions that differed from the trained ones either only in sound frequency (second row) or temporal interval (third and fourth rows). Error bars denote ±1 standard error of the (group) mean. The dashed boxes denote that the trained group learned significantly more than the control group on that condition.

Figure 2. Amount of improvement between the pre- and post-test sessions vs. initial performance for both the “better” (top) and “poorer” (bottom) of the two trained conditions. Results are shown for the interleaved (left column) consecutive (right column) and control (both columns) groups

For both trained listeners (filled symbols) and controls (open symbols), the “better” condition was defined as the trained condition on which the difference between the pre- and post-test thresholds was the larger of the two. Listeners who improved more on the 100-ms condition are denoted with squares, those who improved more on the 350-ms condition are denoted with diamonds. Conditions in which trained listeners learned significantly more than controls are marked with * for p < 0.05 and ** for p < 0.01; n.s. indicates that there was no significant difference in improvement between the two groups.

Figure 3. Group learning curves on average performance (top) and within-listener consistency (bottom)

Results are shown for the interleaved (triangles) and consecutive (circles) groups for the 100-ms (left column) and the 350-ms (right column) conditions. For each listener, the two performance indices are defined as the mean (average performance) or standard deviation (within-listener consistency) of all threshold estimates completed for a particular condition during a single session. See Table 1 for the results of statistical analyses of these data.