The type of processing–resource allocation (TOPRA) model predicts that increasing one type of processing (semantic, structural, or mapping oriented) can decrease other types of processing and their learning counterparts. This study examined how semantic and structural tasks affect the mapping component of second language (L2) vocabulary learning. Japanese-speaking L2 English learners attempted to map secondary meanings of 24 English homographs. Each participant studied them (a) while making pleasantness ratings about word meaning (mapping plus semantic processing); (b) while counting letters in each word (mapping plus structural processing); and (c) without any additional task (mapping only). Results of L1 (first language) and L2 free recalls and L2-to-L1 and L1-to-L2 cued recalls indicated higher free recall in the semantic condition over the structural condition and higher cued recall in the mapping condition over the semantic and structural conditions, providing qualitatively new evidence for TOPRA model predictions.

Previous studies (Barcroft & Sommers, 2005; Sommers & Barcroft, 2007) have demonstrated that variability in talker, speaking style, and speaking rate positively affect second language vocabulary learning, whereas variability in overall amplitude and fundamental frequency (F0) do not, at least for native English speakers. Sommers and Barcroft (2007) hypothesized that English speakers do not benefit (with regard to second language vocabulary learning) from amplitude and F0 variability because these are not phonetically relevant to them. The present study further tested this hypothesis by examining effects of F0 variability among adults who speak a tone language (Zapotec-Spanish bilinguals) and those who do not speak a tone language (Spanish speakers with substantial knowledge of English). Participants attempted to learn 24 Russian words while hearing the words and viewing their corresponding pictures. Three levels of F0 variability were compared. Fundamental frequency variability significantly improved vocabulary learning for speakers of the tone language (Zapotec) but not for the Spanish speakers. This result provides strong evidence that effects of acoustic variability on learning new word forms depend on phonetic relevance.

Research has demonstrated that second language (L2) vocabulary learning improves when target words are presented in acoustically varied compared with acoustically consistent formats. The present study investigated the extent to which this benefit of acoustic variability is a consequence of difficult encoding demands (cognitive effort hypothesis) versus increased representational quality. Experiment 1 compared L2 vocabulary learning for words produced in normal (easier encoding) or nasal (more difficult encoding) voice. Vocabulary learning was superior in the normal-voice condition, arguing against a simple cognitive effort hypothesis as the basis for improved L2 vocabulary learning with increased acoustic variability. Experiment 2 assessed the resistance of newly acquired L2 word forms to the effects of acoustic degradation. Participants heard six repetitions of each item in either a single-talker or multiple-talker condition. The robustness of the new word-form representations was assessed by measuring the accuracy and latency of L2 to first language (L1) translation as a function of the signal/noise ratio. At all four signal/noise ratios, accuracy and latency of L2 to L1 translation were significantly better for words learned in the multiple-talker as opposed to the single-talker condition. Of particular importance, the difference between single talkers and multiple talkers increased systematically as signal/noise ratio decreased. These findings suggest that the benefits of acoustic variability are a consequence of learners' ability to retain and use indexical information during the earliest stages of word learning and provide support for the representation quality hypothesis.

This study examined how three different sources of stimulus variability—overall amplitude, fundamental frequency, and speaking rate—affect second language (L2) vocabulary learning. Native English speakers learned Spanish words in presentation formats with no variability, moderate variability, and high variability. Dependent measures were accuracy and latency of picture-to-Spanish and Spanish-to-English recall. The findings indicated that variability sources that do not affect first language (L1) word identification (amplitude, fundamental frequency) do not affect L2 vocabulary learning. Conversely, variability in speaking rate, which negatively affects L1 word identification, positively affected L2 vocabulary learning. These findings are consistent with an integrated account in which sources of variability that affect phonetically relevant properties of speech impede L1 speech processing but improve L2 vocabulary learning.

This study examined the effects of acoustic variability on second language vocabulary learning. English native speakers learned new words in Spanish. Exposure frequency to the words was constant. Dependent measures were accuracy and latency of picture-to-Spanish and Spanish-to-English recall. Experiment 1 compared presentation formats of neutral (conversational) voice only, three voice types, and six voice types. No significant differences emerged. Experiment 2 compared presentation formats of one speaker, three speakers, and six speakers. Vocabulary learning was superior in the higher-variability conditions. Experiment 3 partially replicated Experiment 1 while rotating voice types across subjects in moderate and no-variability conditions. Vocabulary learning was superior in the higher variability conditions. These results are consistent with an exemplar-based theory of initial lexical learning and representation.Portions of these data were presented at the 143rd meeting of the Acoustical Society of America in Cancun, Mexico and at the Fourth International Conference on the Mental Lexicon in Windsor, Canada. The authors would like to thank Paola Rijos for help in data collection and scoring and the anonymous SSLA reviewers.