Is sleep playing a role in the consolidation of new phonological categories?

Since a long time, studies have shown that the perception of nonnative phonological contrasts is improved after a short period of auditory training and retained over a long period of time after the end of training. However, the role of sleep in the consolidation of this type learning remains debated. In the present study, we investigated the role of post-training sleep in the consolidation of new phonological categories. Adult French-speakers were trained to identify two synthetic speech variants of the syllable /də/ during two 1-h training sessions. The 12-h interval between the two sessions included either a sleep (8 pm to 8 am +or- 1h) or a wake (8 am to 8 pm +or- 1 h) period. Results showed that identification dramatically improved over the first training session in both groups, and then slightly decreased over the 12-h offline interval to remain above chance levels. The analysis of reaction times (RT) showed slowed down responses after sleep as compared to wakefulness, suggesting higher attention devoted to the novel phonological stimulus. Notwithstanding, our results essentially suggest that post-training sleep does not benefit more than wakefulness to the consolidation of new phonological categories.