Brain Structure Predicts the Learning of Foreign Speech Sounds

Abstract

Previous work has shown a relationship between parietal lobe anatomy and nonnative speech sound learning. We scanned a new group of phonetic learners using structural magnetic resonance imaging and diffusion tensor imaging. Voxel-based morphometry indicated higher white matter (WM) density in left Heschl's gyrus (HG) in faster compared with slower learners, and manual segmentation of this structure confirmed that the WM volume of left HG is larger in the former compared with the latter group. This finding was replicated in a reanalysis of the original groups tested in Golestani and others (2002, Anatomical correlates of learning novel speech sounds. Neuron 35:997-1010). We also found that faster learners have a greater asymmetry (left > right) in parietal lobe volumes than slower learners and that the right insula and HG are more superiorly located in slower compared with faster learners. These results suggest that left auditory cortex WM anatomy, which likely reflects auditory processing efficiency, partly predicts individual differences in an aspect of language learning that relies on rapid temporal processing. It also appears that a global displacement of components of a right hemispheric language network, possibly reflecting individual differences in the functional anatomy and lateralization of language processing, is predictive of speech sound learning.

Auditory Cortex Signs of Age-Related Hearing Loss

“…The word recognition effects appeared to be due in part to normal variation in auditory cortex morphology because the association was present within groups of younger and older adults who had clinically normal hearing. These results are consistent with evidence that normal variation Heschl's gyrus morphology is associated with language and music expertise (Golestani et al 2002;Schneider et al 2002;Gaser and Schlaug 2003;Schneider et al 2005;Golestani et al 2007;Wong et al 2008). The Harris et al (2009) effects could have been amplified by subclinical high frequency hearing loss, however.…”

Individual differences in the acquisition of second language phonology

“…We found that only half of the participants improved over the course of this much longer training (Golestani & Zatorre, 2004). Further, in two, related anatomical magnetic resonance imaging (aMRI) studies, it was found that people who are faster at learning to hear the dental-retroflex contrast have a greater left > right asymmetry in parietal lobe white matter volumes (Golestani et al, 2002), as well greater white matter volumes of left Heschl's gyrus, a part of the brain which includes primary auditory cortex (Golestani et al, 2007) than do slower learners. The left inferior parietal cortex has previously been shown to be involved in aspects of phonological processing (Démonet, Price, Wise, & Frackowiak, 1994;Démonet et al, 1992;Zatorre, Evans, Meyer, & Gjedde, 1992;Zatorre, Meyer, Gjedde, & Evans, 1996), and in particular in the storage of phonological information in verbal short-term memory (Jonides et al, 1998;Paulesu, Frith, & Frackowiak, 1993).…”

“…Individual differences were characterized by reporting performance variability, and by examining relationships between measures of preand post-training identification and discrimination test performance, as well as between these test measures and measures of performance during training. We also showed that such individual differences predict individual differences in brain structure in two other studies (Golestani, Molko, Dehaene, LeBihan, & Pallier, 2007;Golestani, Paus, & Zatorre, 2002). Second, in order to elucidate the specificity of the learning, we trained the same individuals to learn to hear a pitch difference between steady-state tones, and compared post-training performance on the speech and tonal stimuli.…”

Brain potentials to native phoneme discrimination reveal the origin of individual differences in learning the sounds of a second language

“…For example, in training studies, participants learn to discriminate new nonnative contrasts under strict laboratory conditions (quiet environments, attention focused on the stimuli) with carefully selected stimuli (highly simplified consonant-vowel sequences, synthesized speech) and procedures (the use of reward or feedback during training), and in relatively short periods of training [e.g., Ͻ30 min (ref. [5][6][7]]. In contrast, in natural situations, the L2 learning is achieved in the context of exposure to very varied stimuli (different speakers, rates of speaking, dialectal variation) without explicit attention being paid to the subtle physical differences entailed in phoneme contrasts and across long-term exposures (usually spanning several years).…”