A limit on behavioral plasticity in speech perception

It is well attested that we perceive speech through the filter of our native language: a classic example is that of Japanese listeners who cannot discriminate between the American /l/ and /r/ and identify both as their own /r/ phoneme (Goto, H., 1971. Neuropsychologia 9, 317-323.). Studies in the laboratory have shown, however, that perception of non-native speech sounds can be learned through training (Lively, S.E., Pisoni, D.B., Yamada, R.A., Tohkura, Y.I., Yamada, T., 1994. Journal of the Acoustical Society of America 96 (4), 2076-2087). This is consistent with neurophysiological evidence showing considerable experience-dependent plasticity in the brain at the first levels of sensory processing (Edeline, J.-M., Weinberger, N.M., 1993. Behavioral Neuroscience 107, 82-103; Merzenich, M.M., Sameshima, K., 1993. Current Opinion in Neurobiology 3, 187-196; Weinberger, N.M., 1993. Current Opinion in Neurobiology 3, 577-579; Kraus, N., McGee, T., Carrel, T.D., King, C., Tremblay, K., Nicol, T., 1995. Journal of Cognitive Neuroscience 7 (1), 25-32). Outside of the laboratory, however, the situation seems to differ: we here report a study involving Spanish-Catalan bilingual subjects who have had the best opportunities to learn a new contrast but did not do it. Our study demonstrates a striking lack of behavioral plasticity: early and extensive exposure to a second language is not sufficient to attain the ultimate phonological competence of native speakers.