Enhancing speech learning by combining task practice with periods of stimulus exposure without practice

Abstract

Language acquisition typically involves periods when the learner speaks and listens to the new language, and others when the learner is exposed to the language without consciously speaking or listening to it. Adaptation to variants of a native language occurs under similar conditions. Here, speech learning by adults was assessed following a training regimen that mimicked this common situation of language immersion without continuous active language processing. Experiment 1 focused on the acquisition of a novel phonetic category along the voice-onset-time continuum, while Experiment 2 focused on adaptation to foreign-accented speech. The critical training regimens of each experiment involved alternation between periods of practice with the task of phonetic classification (Experiment 1) or sentence recognition (Experiment 2) and periods of stimulus exposure without practice. These practice and exposure periods yielded little to no improvement separately, but alternation between them generated as much or more improvement as did practicing during every period. Practice appears to serve as a catalyst that enables stimulus exposures encountered both during and outside of the practice periods to contribute to quite distinct cases of speech learning. It follows that practice-plus-exposure combinations may tap a general learning mechanism that facilitates language acquisition and speech processing.

FIG. 1.

Acquisition of a non-native category boundary. (A) Mean performance across tests. Mean slope of the non-native category boundary between “mba” and “ba” for native speakers of English across daily pre- and post-training tests for each of four two-session training regimens: Exposure-Only (open triangles; n = 8), Practice + Silence (open squares; n = 8), Practice-Only (open diamonds; n = 7), and Practice + Exposure (filled circles; n = 8). Each box in the schematics represents 60 trials of practice (black boxes), 60 trials of stimulus exposure without practice (gray boxes), or the time span of 60 trials spent in silence (white boxes). The slope of the function is scaled such that the closer the value is to zero, the sharper the category boundary. Error bars indicate + /− one standard error of the mean. Slopes are adjusted to account for individual differences in the slope at pre-training test 1. (B) Individual performance. Raw scaled category boundary slopes between “mba” and “ba” from the day 1 pre-training test (abscissa) and day 2 post-training test (ordinate) for each individual listener. Performance of the Practice + Exposure group (filled circles) is shown with that of the Exposure-Only (left panel; open triangles), Practice + Silence (middle panel; open squares), and Practice-Only (right panel; open diamonds) groups. The key result is that a combination of practice categorizing speech tokens with additional exposures to those tokens without practice (Practice + Exposure) facilitated the acquisition of a non-native category boundary. Learning with this combination was enhanced relative to when the training involved only brief (Practice + Silence) or longer (Practice-Only) periods of categorization practice, even though mere exposure to the speech tokens (Exposure-Only) yielded no learning.

FIG. 2.

Adaptation to foreign-accented speech. Percent-correct performance for key words transcribed from spoken Mandarin-accented English sentences by native speakers of English following each of five two-session training regimens: Practice-Only-No-Foreign-Accent-Control, Exposure-Only, Practice + Silence, Practice + Exposure, and Practice-Only (n = 10 per group). Results from the sole post-training test on day 2 are shown for each individual listener (open circles) as well as for the mean of each group (horizontal lines). Error bars indicate +/− one standard error of the mean. The two groups marked with asterisks performed similarly to each other, but significantly better than the other three groups (*p ≤ 0.04; **p ≤ 0.01). The key result is that a combination of practice transcribing foreign-accented sentences combined with additional exposures to those sentences (Practice + Exposure) aided speech recognition of sentences with that accent. Learning with this combination was enhanced relative to when the training involved only brief (Practice + Silence) periods of sentence transcription or mere exposure to foreign-accented sentences (Exposure-Only), and yielded as much improvement as did transcribing all of the sentences (Practice-Only).