Adults’ and Infants’ Perception of Pitch-Evoking Stimuli with No Resolvable Spectral Cues

Abstract

<p>Pitch perception depends on two types of cues provided by acoustic stimuli: spectral cues arise from the tonotopic organization of the basilar membrane, while temporal cues are contained within the pattern of action potentials generated in auditory nerve fibers. Filtered iterated rippled noise (IRN) can be used to examine how adults and infants perceive stimuli without resolvable spectral cues. Chapter 2 uses event-related potentials (ERPs) to compare adult perception of IRN and complex harmonic stimuli. Functional imaging studies have revealed a common pitch centre along lateral Heschl’s gyrus, but lack the temporal resolution to index different stages of processing. Chapter 2 reveals differences between feature extraction-related ERP components elicited in response to different pitch-evoking stimuli. However, no differences were observed in the mismatch negativities (MMN), suggesting pitch percepts formed at this stage of processing are independent of stimulus type. Moreover, source estimates for the MMN were consistent with fMRI studies. Chapter 3 demonstrates that infants can perceive the pitch of stimuli that lack resolvable spectral cues. Eight-month-old infants discriminated between 167 Hz and 200 Hz IRN stimuli. However, performance was poor relative to when resolvable spectral cues were present, and required a period of pitch-priming (Experiment 2). Chapter 4 uses ERPs to further examine infants’ perception of IRN. Using an oddball paradigm, 4- and 8-month-old infants were shown to discriminate between 167 Hz and 200 Hz stimuli. However, successful discriminations again required pitch-priming (Experiment 2). Together, these findings suggest that infant pitch percepts are dominated by resolved spectral cues. Infants discriminate between stimuli without resolvable spectral cues, but appear to require a period of priming to do so, at least until 8 months of age. Thus, infant pitch perception may be impaired in challenging listening situations, such as extracting vocal pitch cues in the presence of background noise.</p>