Profiling the Longitudinal Development of Babbling in Infants with Cerebral Palsy: Validation of the Infant Monitor of Vocal Production (IMP) Using the Stark Assessment of Early Vocal Development-Revised (SAEVD-R)

Aim: We compared early vocal development in children "at risk" for cerebral palsy (CP) with typically developing (TD) infants aged 6 to 15 months using the SAEVD-R, investigating potential pre-linguistic markers of communication impairment. Additionally, we sought to examine the agreement between the SAEVD-R and IMP, which uses parent report, in identifying departure from typical vocal development in at-risk infants. Method: Utilising a longitudinal cohort study, >10,000 vocalisations of 33 infants (15 at risk for CP and 18 TD) were assessed at 6, 9, 12, and 15 months using the SAEVD-R. Generalised linear mixed models (GLMMs) compared groups, and Spearman correlations explored IMP ceiling scores and SAEVD-R measures. Results: At 6 months, both TD and CP groups reached SAEVD-R vocalisation level 3 (expansion). By 9 months, 51% of TD infants progressed to advanced babbling (levels 4 and 5), while 80% of at-risk infants remained at level 3. At 12 and 15 months, over 90% of TD children advanced, compared to 67% at 12 months and 53% at 15 months for at-risk infants, who stayed at the pre-canonical stage. Strong correlations were found between IMP scores and vocalisation levels at 9 and 12 months. Remaining at the pre-canonical stage at 12 months correlated with delayed vocal development as per IMP scores. Interpretation: TD infants achieved higher SAEVD-R levels than at-risk infants. At 12 months, IMP scores effectively identified infants with speech-like vocalisation difficulties, demonstrating its clinical utility in identifying atypical vocal development in infants at risk for CP.