Constraints on the transfer of perceptual learning in accented speech

Abstract

The perception of speech sounds can be re-tuned through a mechanism of lexically driven perceptual learning after exposure to instances of atypical speech production. This study asked whether this re-tuning is sensitive to the position of the atypical sound within the word. We investigated perceptual learning using English voiced stop consonants, which are commonly devoiced in word-final position by Dutch learners of English. After exposure to a Dutch learner's productions of devoiced stops in word-final position (but not in any other positions), British English (BE) listeners showed evidence of perceptual learning in a subsequent cross-modal priming task, where auditory primes with devoiced final stops (e.g., "seed", pronounced [si:t(h)]), facilitated recognition of visual targets with voiced final stops (e.g., SEED). In Experiment 1, this learning effect generalized to test pairs where the critical contrast was in word-initial position, e.g., auditory primes such as "town" facilitated recognition of visual targets like DOWN. Control listeners, who had not heard any stops by the speaker during exposure, showed no learning effects. The generalization to word-initial position did not occur when participants had also heard correctly voiced, word-initial stops during exposure (Experiment 2), and when the speaker was a native BE speaker who mimicked the word-final devoicing (Experiment 3). The readiness of the perceptual system to generalize a previously learned adjustment to other positions within the word thus appears to be modulated by distributional properties of the speech input, as well as by the perceived sociophonetic characteristics of the speaker. The results suggest that the transfer of pre-lexical perceptual adjustments that occur through lexically driven learning can be affected by a combination of acoustic, phonological, and sociophonetic factors.

Keywords: cross-modal priming; foreign-accented speech; perceptual learning; speech.

Figure 1

Priming effects (reaction times in the unrelated minus the related prime type) are shown for each of the four word types, for experimental and control groups, in Experiment 1. The group differences for the /d/-final and /d/-initial word types illustrate learning for word-final position and generalization to word-initial position, respectively. Starred differences denote a significant interaction of group and prime type (related vs. unrelated).

Figure 2

Priming effects in Experiment 2, showing a group difference for the /d/-final words type but no other word type. Starred differences denote a significant interaction of group and prime type (related vs. unrelated).

Figure 3

Priming effects in Experiment 3. As in Experiment 2, there was a group difference for /d/-final words type but no other word type. Starred differences denote a significant interaction of group and prime type (related vs. unrelated).

Figure 4

Spectrograms of the words “pod” and “pot” as produced by the native English (left panels) and the Dutch speaker (right panels).

Figure 5

Duration measurements for both speakers across all minimal pairs with word-final stops in the experiments, shown separately for the voiced and unvoiced members of a pair (e.g., “pod” vs. “pot”). Duration distinctions made by the native speaker were reduced or absent for the Dutch speaker in the case of preceding vowel and closure, but mostly preserved for burst and aspiration. Error bars represent standard deviations.