Against the clock: How time of day influences speech-motor learning in adolescents and young adults with and without childhood apraxia of speech.

The long-term implications of childhood apraxia of speech (CAS) beyond childhood are relatively unknown. This research tracks production performance of a non-native vowel contrast following morning and evening training in adolescents and young adults with and without long-standing CAS. 82 participants aged 12-21 years trained in production of Danish vowels [y] and [ø] in either the morning or evening and completed post-training and 12-hour retention probes. Aligned with previous work, we found that for those with typical speech profiles (TP), offline changes were modulated by time of day of training: whereas evening trainees subtly improved, morning-trained participants declined in accuracy over the 12-hour post-training interval. For those with long-standing CAS, those trained in the morning out-performed evening-trained learners across time. Together, these findings suggest a different trajectory of speech-motor learning and consolidation in adolescents and young adults with a history of CAS.