Infant Pitch and Timbre Discrimination in the Presence of Variation in the Other Dimension

Cortical substrates of perceptual confusion between pitch and timbre

Pitch and timbre are two fundamental perceptual attributes of sound that help us distinguish voices in speech and appreciate music. Brightness, one of the primary dimensions of timbre, is governed by different acoustic parameters compared to pitch, but the two can be confused perceptually when varied simultaneously. Here we combine human behavior and fMRI to provide evidence of a potential neural substrate to explain this important but poorly understood perceptual confusion. We identify orderly mappings of both pitch and brightness within auditory cortex and reveal two independent lines of evidence for cortical confusion between them. First, the preferred pitch of individual voxels decreases systematically as brightness increases, and vice versa, consistent with predictions based on perceptual confusion. Second, pitch and brightness mapping share a common high-low-high gradient across auditory cortex, implying a shared trajectory of cortical activation for changes in each dimension. The results provide a cortical substrate at both local and global scales for an established auditory perceptual phenomenon that is thought to reflect efficient coding of features ubiquitous in natural sound statistics.

Pitch perception in school-aged children: Pure tones, resolved and unresolved harmonics

Pitch perception affects children's ability to perceive speech, appreciate music, and learn in noisy environments, such as their classrooms. Here, we investigated pitch perception for pure tones as well as resolved and unresolved complex tones with a fundamental frequency of 400 Hz in 8- to 11-year-old children and adults. Pitch perception in children was better for resolved relative to unresolved complex tones, consistent with adults. The younger 8- to 9-year-old children had elevated thresholds across all conditions, while the 10- to 11-year-old children had comparable thresholds to adults.

Effect of Hearing Aids on Phonation and Perceived Voice Qualities

Problems with own-voice sounds are common in hearing aid users. As auditory feedback is used to regulate the voice, it is possible that hearing aid use affects phonation. The aim of this paper is to compare hearing aid users' perception of their own voice with and without hearing aids and any effect on phonation. Eighty-five first-time and 85 experienced hearing aid users together with a control group of 70 completed evaluations of their own recorded and live voice in addition to two external voices. The participants' voice recordings were used for acoustic analysis. The results showed moderate to severe own-voice problems (OVP) in 17.6% of first-time users and 18.8% of experienced users. Hearing condition was a significant predictor of the perception of pitch in external voices and of monotony, lower naturalness, and lower pleasantness in their own live voice. The groups with hearing impairment had a higher mean fundamental frequency (f0) than the control group. Hearing aids decreased the speaking sound pressure level by 2 dB on average. Moreover, acoustic analysis shows a complex relationship between hearing impairment, hearing aids, and phonation and an immediate decrease in speech level when using hearing aids. Our findings support previous literature regarding auditory feedback and voice regulation. The results should motivate clinicians in hearing and voice care to routinely take hearing functions into account when assessing voice problems.

A unitary model of auditory frequency change perception

Changes in the frequency content of sounds over time are arguably the most basic form of information about the behavior of sound-emitting objects. In perceptual studies, such changes have mostly been investigated separately, as aspects of either pitch or timbre. Here, we propose a unitary account of "up" and "down" subjective judgments of frequency change, based on a model combining auditory correlates of acoustic cues in a sound-specific and listener-specific manner. To do so, we introduce a generalized version of so-called Shepard tones, allowing symmetric manipulations of spectral information on a fine scale, usually associated to pitch (spectral fine structure, SFS), and on a coarse scale, usually associated timbre (spectral envelope, SE). In a series of behavioral experiments, listeners reported "up" or "down" shifts across pairs of generalized Shepard tones that differed in SFS, in SE, or in both. We observed the classic properties of Shepard tones for either SFS or SE shifts: subjective judgements followed the smallest log-frequency change direction, with cases of ambiguity and circularity. Interestingly, when both SFS and SE changes were applied concurrently (synergistically or antagonistically), we observed a trade-off between cues. Listeners were encouraged to report when they perceived "both" directions of change concurrently, but this rarely happened, suggesting a unitary percept. A computational model could accurately fit the behavioral data by combining different cues reflecting frequency changes after auditory filtering. The model revealed that cue weighting depended on the nature of the sound. When presented with harmonic sounds, listeners put more weight on SFS-related cues, whereas inharmonic sounds led to more weight on SE-related cues. Moreover, these stimulus-based factors were modulated by inter-individual differences, revealing variability across listeners in the detailed recipe for "up" and "down" judgments. We argue that frequency changes are tracked perceptually via the adaptive combination of a diverse set of cues, in a manner that is in fact similar to the derivation of other basic auditory dimensions such as spatial location.

The development of auditory temporal processing during the first year of life

Objectives

The processing of auditory temporal information is important for the extraction of voice pitch, linguistic information, as well as the overall temporal structure of speech. However, many aspects of its early development remain poorly understood. This paper reviews the development of auditory temporal processing during the first year of life when infants are acquiring their native language.

Methods

First, potential mechanisms of neural immaturity are discussed in the context of neurophysiological studies. Next, what is known about infant auditory capabilities is considered with a focus on psychophysical studies involving non-speech stimuli to investigate the perception of temporal fine structure and envelope cues. This is followed by a review of studies involving speech stimuli, including those that present vocoded signals as a method of degrading the spectro-temporal information available to infant listeners.

Results/Conclusion

This review suggests that temporal resolution may be well developed in the first postnatal months, but that the ability to use and process the temporal information in an efficient way along the entire auditory pathway is longer to develop. Those findings have crucial implications for the development of language abilities, especially for infants with hearing impairment who are using cochlear implants.