Study on the Language Formation Process of Very-Low-Birth-Weight Infants in Infancy Using a Formant Analysis

Expressive language development depends on anatomical factors, such as motor control of the tongue and oral cavity needed for vocalization, as well as cognitive aspects for comprehension and speech. The purpose of this study was to examine the differences in expressive language development between normal-birth-weight (NBW) infants and very-low-birth-weight (VLBW) infants in infancy using a formant analysis. We also examined the presence of differences between infants with a normal development and those with a high risk of autism spectrum disorder who were expected to exist among VLBW infants. The participants were 10 NBW infants and 10 VLBW infants 12-15 months of age whose speech had been recorded at intervals of approximately once every 3 months. The recorded speech signal was analyzed using a formant analysis, and changes due to age were observed. One NBW and 3 VLBW infants failed to pass the screening tests (CBCL and M-CHAT) at 24 months of age. The formant frequencies (F1 and F2) of the three groups of infants (NBW, VLBW and CBCL·M-CHAT non-passing infants) were scatter-plotted by age. For the NBW and VLBW infants, the area of the plot increased with age, but there was no significant expansion of the plot area for the CBCL·M-CHAT non-passing infants. The results showed no significant differences in expressive language development between NBW infants at 24 months old and VLBW infants at the corrected age. However, different language developmental patterns were observed in CBCL·M-CHAT non-passing infants, regardless of birth weight, suggesting the importance of screening by acoustic analyses.