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. 2012 May;49(5):720-31.
doi: 10.1111/j.1469-8986.2011.01353.x. Epub 2012 Feb 14.

Influence of gestational age and postnatal age on speech sound processing in NICU infants

Alexandra P F Key  1 , E Warren Lambert, Judy L Aschner, Nathalie L Maitre
Affiliations

Influence of gestational age and postnatal age on speech sound processing in NICU infants

Alexandra P F Key et al. Psychophysiology. 2012 May.

Abstract

The study examined the effect of gestational (GA) and postnatal (PNA) age on speech sound perception in infants. Auditory event-related potentials (ERPs) were recorded in response to speech sounds (syllables) in 50 infant NICU patients (born at 24-40 weeks gestation) prior to discharge. Efficiency of speech perception was quantified as absolute difference in mean amplitudes of ERPs in response to vowel (/a/-/u/) and consonant (/b/-/g/, /d/-/g/) contrasts within 150-250, 250-400, 400-700 ms after stimulus onset. Results indicated that both GA and PNA affected speech sound processing. These effects were more pronounced for consonant than vowel contrasts. Increasing PNA was associated with greater sound discrimination in infants born at or after 30 weeks GA, while minimal PNA-related changes were observed for infants with GA less than 30 weeks. Our findings suggest that a certain level of brain maturity at birth is necessary to benefit from postnatal experience in the first 4 months of life, and both gestational and postnatal ages need to be considered when evaluating infant brain responses.

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Figures

Figure 1
Figure 1
Electrode layout and selected clusters used in the study.
Figure 2
Figure 2
Descriptive statistics: gestational age (weeks), postnatal age at ERP (months), and ERP differences (µV).
Figure 3
Figure 3
Average ERP waveforms for consonant contrasts in infants with gestational age (A) less than 30 weeks; (B) over 30 weeks.
Figure 4
Figure 4
Significant (p < .05) effects of gestational age and postnatal age. Note: Figure shows mean absolute discrimination scores (µV) as a function of gestational age and postnatal age. Error bars show 95% confidence intervals. For illustration purposes only, postnatal age was dichotomized with a median split (1.97 months). Gestational age was dichotomized at 30 weeks. Significance tests were done with continuous data, as shown in Table 1.
Figure 5
Figure 5
Significant (p < .05) three-way GA * PNA Interactions Note: Figure shows GA*PNA interactions with hemisphere, location, and time window. Each point represents a mean absolute difference (µV). For illustration purposes only, postnatal age was dichotomized with a median split (1.97 months). Gestational age was dichotomized at 30 weeks. Significance tests were done with continuous data, as shown in Table 1. Confidence intervals were wide but are not marked to improve figure clarity.
Figure 6
Figure 6
Significant GA and PNA Main Effects and Interaction Panels A & B are main effects, the effect of a single variable on discrimination. Panel C shows the interaction, the combined effect of GA and PNA, calculated as the product of the two variables. As seen in Panel C, the interaction is an increase in discrimination ability when both GA and PNA are high. These three effects are orthogonal (statistically independent) in the sense of making distinct contributions to speech discrimination ability.
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