Development and validation of a language learning model for behavioral and functional-imaging studies.
To obtain a more precise understanding of the mechanisms involved in language acquisition in healthy subjects and the re-acquisition of language following brain damage, we developed a word learning model which can be used in behavioral and functional-imaging studies. We generated a set of spoken pseudowords, which were normalized with respect to duration and loudness, and (based on a rating study with 40 students) selected 50 pseudowords, which yielded few associations with existing words and were of neutral emotional valence. The selected pseudowords were paired with object drawings in a pseudo-randomized manner and each subject received a different combination of pairings. These auditory-visual pairs were used to train ten subjects solely on the basis of different frequencies of 'correct' and 'incorrect' pairings. This procedure resembles the acquisition of the first words during childhood. During a five-session training protocol, with one session per day, there was a linear increase of the learning curves, which then reached a plateau. Learning remained stable at 1 and 4 weeks retest intervals. Furthermore, subjects correctly translated the pseudowords into their native language, demonstrating the acquisition of word meanings. These findings indicate that the described associative learning program meets the requirements for a robust and ecologically meaningful model to study the neural mechanisms of language learning and plasticity.