Vocalization patterns distinguish toddlers later diagnosed with autism from TD at 18-23 months

In this cross-sectional study with prospective diagnostic follow-up, vocalizations of infants and toddlers later diagnosed with autism spectrum disorder (ASD) and typically developing (TD) controls (aged 6-23 months) were coded frame-by-frame during a single Still-Face paradigm into four categories: directed; nondirected; speech-like; and non-speech-like vocalizations. We examined their relationship with the Language Development Quotient (LDQ). After FDR correction for multiple comparisons, two vocal patterns showed robust differences exclusively in the 18-23-month window: (1) directed vocalization frequency was significantly higher in TD versus ASD, and (2) nondirected vocalization duration was significantly longer in ASD versus TD, both with large effect sizes. Differences in the 6-10-and 11-17-month groups did not survive correction. Conclusions: The late divergence pattern-minimal differences in directed and nondirected vocalizations before 18 months, significant amplification at 18-23 months-identifies this window as a critical period for screening and early intervention in ASD, when social-communicative vocal patterns diverge most substantially from typical development. The findings suggest that directed vocalizations may serve as a possible low-cost behavioral marker distinguishing ASD from typical development, and that speech-like vocalizations show age-dependent associations with language outcomes, defining 18-23 months as a sensitive window for screening and early intervention.