Individual differences in the acquisition of second language phonology Narly Golestani a,b,c, * , Robert J. Zatorre a a Cognitive Neuroscience Unit/Montreal Neurological Institute, McGill University, Montreal, Que., Canada b Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK c Functional Brain Mapping Laboratory, Neurology Clinic, University Medical School, 24 rue Micheli-du-Crest 1211 Geneva, Switzerland Accepted 14 January 2008 Available online 4 March 2008 Abstract Perceptual training was employed to characterize individual differences in non-native speech sound learning. Fifty-nine adult English speakers were trained to distinguish the Hindi dental–retroflex contrast, as well as a tonal pitch contrast. Training resulted in overall group improvement in the ability to identify and to discriminate the phonetic and the tonal contrasts, but there were considerable indi- vidual differences in performance. A category boundary effect during the post-training discrimination of the Hindi but not of the tonal contrast suggests different learning mechanisms for these two stimulus types. Specifically, our results suggest that successful learning of the speech sounds involves the formation of a long-term memory category representation for the new speech sound. Ó 2008 Elsevier Inc. All rights reserved. Keywords: Phonetic learning; Behavioral plasticity; Language; Individual differences; Non-native; Hindi dental–retroflex contrast 1. Introduction During adulthood, most individuals perceptually assim- ilate certain non-native speech sounds with similar ones from the native language (Best, McRoberts, & Sithole, 1988). For example, native English speakers typically can- not hear the difference between the English alveolar and the Hindi retroflex stop consonants. So even though native speakers of Indian languages hear the difference as easily as anyone reading this paper can hear the difference between ‘b’ and ‘d’, to native English speakers, both are heard as the voiced alveolar stop consonant ‘d’ (Polka, 1991; Rivera-Gaxiola, Csibra, Johnson, & Karmiloff- Smith, 2000a; Werker & Lalonde, 1988). There is evidence, however, for considerable variability across individuals in the learning of speech sounds that involve rapid spectral change, in particular ones that contrast place of articula- tion, such as the r/l contrast for native Japanese listeners, or the dental–retroflex one for native English speakers. Specifically, even among individuals with similar language backgrounds, some are able to hear these non-native sounds in adulthood, or to learn them quickly with limited training, while for others, learning to hear these sounds is more slow and effortful (Bradlow, Pisoni, Akahane-Yam- ada, & Tohkura, 1997; Golestani & Zatorre, 2004; Polka, 1991; Pruitt, Strange, Polka, & Aguilar, 1990). We address two principal questions in the present study. First, we wanted to characterize individual differences in how well or how quickly English-speaking adults can learn to hear the non-native retroflex sound. Very few studies have attempted to account for individual differences in non-native speech sound learning (Bradlow et al., 1997; Flege, MacKay, & Meador, 1999). Individual differences were characterized by reporting performance variability, and by examining relationships between measures of pre- and post-training identification and discrimination test per- formance, as well as between these test measures and mea- sures of performance during training. We also showed that such individual differences predict individual differences in brain structure in two other studies (Golestani, Molko, 0093-934X/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bandl.2008.01.005 * Corresponding author. Address: Functional Brain Mapping Labora- tory, Neurology Clinic, University Hospital and Department of Funda- mental Neurosciences, University Medical School, 24 rue Micheli-du- Crest 1211 Geneva, Switzerland. Fax: +44 (0) 20 7916 8517. E-mail address: n.golestani@ucl.ac.uk (N. Golestani). www.elsevier.com/locate/b&l Available online at www.sciencedirect.com Brain & Language 109 (2009) 55–67