20150
Acoustic Properties of Affective Vocalizations Produced By Six-Month-Old High- and Low-Risk Infants
Intonation emerges in infancy, at approximately six months, in response to physiological changes to the vocal tract, perceptual biases and linguistic influences within the infant’s environment (Stark et al., 1993). While nuclear intonation provides linguistic information, affective intonation conveys emotion (Cruttenden, 1997). Atypical cry intonation may emerge as young as six months in high-risk infants and may be a precursor of later affective intonation deficits associated with ASD (Sheinkopf et al., 2012). Despite recent literature regarding the vocalizations of high-risk infants, little is known about the acoustic properties of affective vocalizations in this population.
Objectives:
To examine the acoustic properties of affective vocalizations produced by six-month-old high- and low-risk infants.
Methods:
Thirty high-risk (HR) and twenty low-risk (LR) six-month-old infants were recruited from a larger study examining ASD symptoms in the first three years of life. A subset of the sample was coded for this abstract (n = 7), including four high-risk and three low-risk infants. At age three, all HR infants in this subset received an ASD diagnosis, and all LR infants were typically developing (TD). Five-minute speech samples were collected during quasi-naturalistic parent-child interactions (Paul et al., 2010). A research assistant blind to risk status acousticaly coded vocalizations for pitch range and mean fundamental frequency using Praat (Boersma, 2014). Vocalizations were also assigned a perceptual rating of either affective (i.e. positive or negative) or neutral (not conveying affect). Volubility of vocalizations was computed.
Results:
Both groups produced similar proportions of affective (Mhr = 0.69, Mlr = 0.58) and neutral (Mhr = 0.31, Mlr = 0.42) vocalizations. Independent t-tests revealed no significant effect of risk status on volubility for affective (t(5) = -1.35, p = 0.24) or neutral (t(5) = -1.06, p = 0.34) vocalizations. A linear mixed model analysis showed a main effect of affect (F(1, 173.93) = 6.38, p < 0.05; affective > neutral) and a trend toward an effect of risk status (F(1,5.88) = 4.13, p = 0.09; HR > LR) on pitch range. Planned comparisons also suggested trends toward between-group differences in pitch range for affective vocalizations (F(1, 7.45) = 4.67, p = 0.07; HRaffective > LRaffective). An additional linear mixed model revealed a main effect of affect (F(1,158.23) = 19.38, p < 0.001; affective > neutral) and a trend toward an effect of risk status (F(1,5.22) = 3.09, p = 0.14; HR > LR) on mean fundamental frequency.
Conclusions:
These preliminary results reveal intonation trends in the affective vocalizations produced by six-month-old HR infants later diagnosed with ASD. In this subset, HR infants produced higher- and more variably-pitched affective vocalizations. Analyses of the total sample will ascertain whether the observed trends translate into reliable effects. If so, as early as six months, HR infants’ vocalizations may be shown to exhibit acoustic differences that are not evident perceptually (Paul et al., 2010). Ongoing full-sample analyses will include comparisons between 1) affective categories (positive and negative) and 2) diagnostic groups (HR-ASD, HR-BAP (broader autism phenotype), and LR-TD). We will present the full sample at IMFAR.