Effects of practice on variability, effects of variability on transfer.

Five experiments examined how practice early in skill acquisition affected variability and accuracy during skill retention (Experiments 1-5) and skill transfer (Experiments 3, 4, 5). Lag constraints required that each path from apex to base of a computer-generated pyramid display differ from some number (the lag) of immediately prior paths. Location constraints specified end points at which paths must exit the pyramid. In all experiments, an early optimal period for acquiring a variability level was identified. Both low and high levels of variability were sustained during retention; high levels facilitated transfer. The results suggest that (a) early practice that requires high variability sensitizes learners to changes in condition and (b) such perception-performance links facilitate transfer by activating appropriate alternative strategies/schema or initiating their construction.

A dedicated neural mechanism for vowel selection: a case of relative vowel deficit sparing the number lexicon.

We report the case of an Italian speaker (GBC), with classical Wernicke's aphasia following a vascular lesion in the posterior middle temporal region. GBC exhibited a selective deficit in spoken language production affecting vowels more than consonants. In reading from a newspaper, GBC substituted vowels for other vowels from the Italian inventory at a rate of 7/1 compared to consonants. No effects of frequency or grammatical class were found. Vowel errors could also not be accounted for by morphological or known phonological processes. Production of number words, in contrast, was free from phonological errors. While GBC has intact representations of Italian vowels and consonants, his data argue for a separate selection mechanism for vowels that is dissociable from that used for consonants. This case provides neuropsychological evidence for models of word production that distinguish between the abstract phonological properties of a word (e.g., sequencing of phonemic slots, or "CV skeleton") and a separate representation for the specific sounds (melody).