Critical Evidence : A Test of the Critical-Period Hypothesis for Second-Language Acquisition

This study assessed the relation between non-native subjects' age of learning (AOL) English and the overall degree of perceived foreign accent in their production of English sentences. The 240 native Italian (NI) subjects examined had begun learning English in Canada between the ages of 2 and 23 yr, and had lived in Canada for an average of 32 yr. Native English-speaking listeners used a continuous scale to rate sentences spoken by the NI subjects and by subjects in a native English comparison group. Estimates of the AOL of onset of foreign accents varied across the ten listeners who rated the sentences, ranging from 3.1 to 11.6 yr (M = 7.4). Foreign accents were evident in sentences spoken by many NI subjects who had begun learning English long before what is traditionally considered to be the end of a critical period. Very few NI subjects who began learning English after the age of 15 yr received ratings that fell within the native English range. Principal components analyses of the NI subjects' responses to a language background questionnaire were followed by multiple-regression analyses. AOL accounted for an average of 59% of variance in the foreign accent ratings. Language use factors accounted for an additional 15% of variance. Gender was also found to influence degree of foreign accent.

The presence or absence of a particular experience at a particular time in the life cycle may exert an extraordinary and dramatic influence over structure or function well beyond that point in development. Such sensitive periods are thought to be widespread in animal and in human neurobiology and psychology. A comprehensive treatment of the sensitive period needs minimally to include information about its structural characteristics as well as an interpretation of its causes, including why the sensitive period arises in terms of the natural history of the species and how the sensitive period is regulated in terms of physical, physiological, and psychological processes. This article provides a framework for research and theory concerning specific sensitive periods and the sensitive period generally conceived. The framework delimits four sets of parameters, which encompass 14 structural characteristics that define sensitive periods, and two levels of causal interpretation that guide research and theory into sensitive periods however they may be manifested.