Nicole Folland, Blake E Butler, Jennifer E Payne, and Laurel J Trainor (2014)
Cortical Representations Sensitive to the Number of Perceived Auditory Objects Emerge between 2 and 4 Months of Age: Electrophysiological Evidence.
J Cogn Neurosci:1-8.
Sound waves emitted by two or more simultaneous sources reach the ear as one complex waveform. Auditory scene analysis involves parsing a complex waveform into separate perceptual representations of the sound sources (Bregman, A. S. Auditory scene analysis: The perceptual organization of sounds. London: MIT Press, 1990). Harmonicity provides an important cue for auditory scene analysis.Normally, harmonics at integer multiples of a fundamental frequency are perceived as one sound with a pitch corresponding to the fundamental frequency. However, when one harmonic in such a complex, pitch-evoking sound is sufficiently mistuned, that harmonic emerges from the complex tone and is perceived as a separate auditory object. Previous work has shown that the percept of two objects is indexed in both children and adults by the object-related negativity component of the ERP derived from EEG recordings (Alain et al., 2001). Here we examine theemergence of object-related responses to an 8% harmonic mistuning in infants between 2 and 12 months of age. Two-month-old infants showed no significant object-related response. However, in 4- to 12-month-old infants, a significant frontally positive component was present, and by 8-12 months, a significant frontocentral object-related negativity was present, similar to that seen in older children and adults. This is in accordance with previous research demonstrating that infants younger than 4 months of age do not integrate harmonic information to perceive pitch when the fundamental is missing (He, C., Hotson, L., & Trainor, L. J. Maturation of cortical mismatch mismatch responses to occasional pitch change in early infancy: Effects of presentation rate and magnitude of change. Neuropsychologia, 47, 2009, 218-229). The results indicate that the ability to use harmonic information to segregate simultaneous sounds emerges at the cortical level between 2 and 4 months of age.