Study validity criteria, study quality scores and levels of evidence for included articles.

Criteria scoring: 0 = flawed or no information from which to make a judgement, 1 = weak information, incorrect use or lack of detail from which to make a judgement, 2 = appropriate use and reporting. Study quality score = sum of scores for scientific and training-specific study validity criteria. 1. Level of evidence: Study quality score of 0–5 = very low, 6–10 = low, 11–15 = moderate, 16–20 = high (adapted from GRADE Working Group, 2004 [35]). 2. Outcome measure selection: to assess generalisation of learning to untrained measure(s) of speech intelligibility, cognition or communication.