McCarthy, K. 1, 2 , Mair, K. 1 , Skoruppa, K. 3 & Iverson, P. . 1
1 University College London
2 2Queen Mary University of London
3 University of Neuchâtel
In our recent work, we created detailed perceptual maps of infant vowel development using the Acoustic Change Complex (ACC) within EEG. More specifically, we showed that vowel perception development seems to be driven by the low frequency aspects of the speech signal. Such findings could be explained by early auditory experience of low frequencies in the womb (Kisilevsky et al., 2009), and possibly explain the developmental trajectory of vowels being acquired earlier than higher frequency consonant sounds such as fricatives (e.g., Nespor, Pena & Mehler, 2003). The aim of the present study was to explore this hypothesis further by detailing individual differences in vowel and fricative perception throughout the first year of life. A secondary aim was to investigate the relationship between this early auditory processing and later language outcomes. Eighty monolingual English infants (4-5, 7-8 and 10-11 months old) took part in the study. Vowel and fricative sensitivity was assessed using the ACC within EEG, which for infants typically evokes a positivity about 150-200 ms after a spectral change. The ACC was measured for three vowel pairs and three fricative pairs, that were presented in runs of five per pair before switching to a new random pair. ERPs were averaged across epochs for each pair, with the magnitude of the response for each pair being used as a comparison measure. Each infant was tested for an average of 18 minutes, resulting in around 250 trials per pair. In addition, the infants? language skills were assessed at 16, 20, and 24-months using the Oxford CDI.Preliminary results show individual differences for vowel and fricative perception. Infants initially show a greater sensitivity to the vowel contrasts, with fricative sensitivity increasing with age. Further analysis will be conducted to explore which spectral features are driving the infants? perceptual sensitivity. These findings display a more detailed pattern of the speech perception than has been shown before, and demonstrate how the ACC can be used to explore developmental trajectories. The results will be discussed with respect with the infants? later language outcomes, and the possible application of this method in a clinical setting.