Age-limited learning effects in reading and speech perception

Age-limited plasticity is a central issue in cognitive neuroscience. Recently, important advances have been made in understanding the molecular, physiological and anatomical processes that give rise to age-limited plasticity in a number of different animal models. How this understanding might be applied to age-limited learning in humans—particularly sensitive period effects in language learning—has remained largely unexplored, however. The current work represents an attempt to apply insights from other areas of neuroscience to the study of age-limited learning effects in language. In particular, I propose that these effects can be explained in terms of the entrenchment of knowledge that supports one's native language, as opposed to parametric changes in brain plasticity, or specific changes in the function of a specialized “language-acquisition device.”; This approach is applied to two domains of language: word reading and speech perception. In the section on word reading, the literature on age of acquisition (AoA) effects is critically evaluated. A series of models and empirical studies are presented which suggest that previous reports of AoA effects have been due to confounds with other variables. The models suggest a theoretical reason for the lack of such effects in reading. Because word naming relies heavily on the translation from spelling to sound, knowledge of early items transfers readily to performance on late items. This ability to generalize from early to late knowledge eliminates any potential advantage for early learning.; Speech perception provides a natural example of a situation in which early knowledge does not always generalize to later learning. When one tries to acquire a second language, many of the novel speech sounds are familiar, but a small subset of them are often extremely difficult to learn. Models in this section show how the entrenchment of one's native language phonological inventory can limit the ability to learn a second language.