Aptitude for novel speech sounds and sound sequences: Implications for second-language pronunciation

Second language speech accent is remarkably variable in strength ranging from near-native to unintelligible. The age at which one begins learning accounts for -- but does not explain -- a large part of the variance. Age cannot account for the large variation in accent strength among later-learners. Other factors such as motivation, quality of input, and so forth can only explain a little bit of this variation. Much of the difference between individuals seems to be due to some latent talent. This dissertation explores this variation and attempts to find a cognitive correlate or component of this differential aptitude.;The series of experiments first identifies and defines the degree of accent variability as function of age. Next, the degree of spoken accent is related to differences in ability to perceive small phonetic differences as expressed in the accent of other speakers. Next, this is expanded to assess speaker sensitivity to within-category differences between speech sounds related to their language(s) with the idea that differential sensory memory persistence provides the retention mechanism for making fine-grained phonetic distinctions. The relationship between phonetic sensitivity and accent strength is further generalized by employing longer, more naturally complex speech utterances. Finally, the contribution of auditory short-term memory is considered.;These results demonstrate that the relationship between expected accent and age of learning is likely a non-linear sigmoid with turning points around age 6 and age 12. The degree of variability in accent strength scales with the expected value and reaching maximal dispersion before age 12. Much of the variance among later-learner accent strength can be predicted by speaker idiosyncratic sensitivity to phonetic differences as measured by d'. The role of sensory memory as the medium in which phonetic information is differentially stored or processed is demonstrated by changes in sensitivity due to increased inter-stimulus interval or linguistic load. A smaller portion of the accent variability is accounted for by differential short-term memory span. This is attributed to phonological aspects of second language acquisition. These results are consistent with the hypothesis that differential capacity to make fine-phonetic discriminations affects spoken accent and that sensory memory underlies this talent.