A standardised assessment instrument, the Pre-Verbal Communication Schedule (PVCS), will be administered before each subject's first session of Intensive Interaction, and again after her/his 16th session to obtain a global view of non-verbal communicative behaviour. Pre- and post-test scores will be compared. The theoretical basis of both Intensive Interaction and the specific use of adjunctive improvised music is primarily affective, but it is important that any benefits should also be detectable in functional terms, hence the choice of PVCS rather than a more affectively orientated measure.