Cortical Representations Sensitive to the Number of Perceived Auditory Objects Emerge between 2 and 4 Months of Age: Electrophysiological Evidence

• Published in: Journal of cognitive neuroscience Vol. 27; no. 5; pp. 1060 - 1067
• Main Authors: Folland, Nicole A., Butler, Blake E., Payne, Jennifer E., Trainor, Laurel J.
• Format: Journal Article
• Language: English
• Published: One Rogers Street, Cambridge, MA 02142-1209, USA MIT Press 01.05.2015; MIT Press Journals, The
• Subjects: Acoustic Stimulation; Age Factors; Aging - physiology; Auditory Cortex - physiology; Babies; Brain; Brain Mapping; Ears & hearing; Electroencephalography; Evoked Potentials, Auditory - physiology; Female; Harmonic analysis; Humans; Infant; Male; Mathematics; Maturation; Pitch Perception - physiology; Sound
• ISSN: 0898-929X; 1530-8898
• DOI: 10.1162/jocn_a_00764

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. . 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, C., Arnott, S. T., & Picton, T. W. Bottom–up and top–down influences on auditory scene analysis: Evidence from event-related brain potentials. 1072–1089, 2001]. Here we examine the emergence 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. 218–229, 2009]. 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.