Individual Differences in Audio-Vocal Speech Imitation Aptitude in Late Bilinguals: Functional Neuro-Imaging and Brain Morphology

Susanne Maria Reiterer,Xiaochen Hu,Giuseppina Rota,Hermann Ackermann,Davide Nardo,Michael Erb,Susanne Winkler,Wolfgang Grodd

doi:10.3389/fpsyg.2011.00271

Abstract

An unanswered question in adult language learning or late bi and multilingualism is why individuals show marked differences in their ability to imitate foreign accents. While recent research acknowledges that more adults than previously assumed can still acquire a “native” foreign accent, very little is known about the neuro-cognitive correlates of this special ability. We investigated 140 German-speaking individuals displaying varying degrees of “mimicking” capacity, based on natural language text, sentence, and word imitations either in their second language English or in Hindi and Tamil, languages they had never been exposed to. The large subject pool was strictly controlled for previous language experience prior to magnetic resonance imaging. The late-onset (around 10 years) bilinguals showed significant individual differences as to how they employed their left-hemisphere speech areas: higher hemodynamic activation in a distinct fronto-parietal network accompanied low ability, while high ability paralleled enhanced gray matter volume in these areas concomitant with decreased hemodynamic responses. Finally and unexpectedly, males were found to be more talented foreign speech mimics.

Highlights

There are considerable individual differences when it comes to the pronunciation of a foreign language, especially if it is learned in adolescence
For defining our high and low ability groups for the further investigations we used the uppermost and lowest 15% of all participants, which resulted in extreme groups of 20 subjects, corresponding to the range between the first and second SD above and below the mean score
To elucidate the exact group differences, we compared the groups by means of a two way analysis of variance (ANOVA) flexible factorial design

Summary

Introduction

There are considerable individual differences when it comes to the pronunciation of a foreign language, especially if it is learned in adolescence. Research in the field of second language (L2) learning ability/aptitude (Obler and Fein, 1988; Skehan, 2011) has established that individuals can either have what the authors call a “talent for accent” (phonetic/phonological domain) or a “talent for grammar” (syntactic–semantic domain, Nauchi and Sakai, 2009). Those who have a talent for accent can imitate foreign speech up to a native level, despite their late age of onset of learning (AOL). A very few attempts to clarify the neural correlates of parts of foreign language imitation capacity have been undertaken (Golestani et al, 2002; Amunts et al, 2004), but 1. no integration of the anatomical and functional bases in one and the same subject sample has been reported so far, 2. collateral variables such as previous language experience have not been controlled rigorously, 3. single cases were reported, or small to medium sample sizes which did not include the upper and lower percentiles of the ability spectrum (very high versus very low ability), 4. sample stimuli employed were confined to single phonemes only (which do not reflect accent imitation in its full range), and 5. in most cases the phonetic level of speech-sound imitation/production capacity was not investigated in isolation ( being confounded with other levels of language)

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