To advance our understanding of the biological basis of speech-in-noise perception, we investigated the effects of background noise on both subcortical- and cortical-evoked responses, and the relationships between them, in normal hearing young adults. The addition of background noise modulated subcortical and cortical response morphology. In noise, subcortical responses were later, smaller in amplitude and demonstrated decreased neural precision in encoding the speech sound. Cortical responses were also delayed by noise, yet the amplitudes of the major peaks (N1, P2) were affected differently, with N1 increasing and P2 decreasing. Relationships between neural measures and speech-in-noise ability were identified, with earlier subcortical responses, higher subcortical response fidelity and greater cortical N1 response magnitude all relating to better speech-in-noise perception. Furthermore, it was only with the addition of background noise that relationships between subcortical and cortical encoding of speech and the behavioral measures of speech in noise emerged. Results illustrate that human brainstem responses and N1 cortical response amplitude reflect coordinated processes with regards to the perception of speech in noise, thereby acting as a functional index of speech-in-noise perception.

The musical priming paradigm has shown facilitated processing for tonally related over less-related targets. However, the congruence between tonal relatedness and the psychoacoustical properties of music challenges cognitive interpretations of the involved processes. Our goal was to show that cognitive expectations (based on listeners' tonal knowledge) elicit tonal priming in melodies independently of sensory components (e.g., spectral overlap). A first priming experiment minimized sensory components by manipulating tonal relatedness with a single note change in the melodies. Processing was facilitated for related over less-related target tones, but an auditory short-term memory model succeeded in simulating this effect, thus suggesting a sensory-based explanation. When the same melodies were played with pure tones (instead of piano tones), the sensory model failed to differentiate between related and less-related targets, while listeners' data continued to show a tonal relatedness effect (Experiment 2). The tonal priming effect observed here thus provides strong evidence for the influence of listeners' tonal knowledge on music processing. The overall findings point out the need for controlled musical material (and notably beyond tone repetition) to study cognitive components in music perception.

The neural mechanisms of pitch coding have been debated for more than a century. The two main mechanisms are coding based on the profiles of neural firing rates across auditory nerve fibers with different characteristic frequencies (place-rate coding), and coding based on the phase-locked temporal pattern of neural firing (temporal coding). Phase locking precision can be partly assessed by recording the frequency-following response (FFR), a scalp-recorded electrophysiological response that reflects synchronous activity in subcortical neurons. Although features of the FFR have been widely used as indices of pitch coding acuity, only a handful of studies have directly investigated the relation between the FFR and behavioral pitch judgments. Furthermore, the contribution of degraded neural synchrony (as indexed by the FFR) to the pitch perception impairments of older listeners and those with hearing loss is not well known. Here, the relation between the FFR and pure-tone frequency discrimination was investigated in listeners with a wide range of ages and absolute thresholds, to assess the respective contributions of subcortical neural synchrony and other age-related and hearing loss-related mechanisms to frequency discrimination performance. FFR measures of neural synchrony and absolute thresholds independently contributed to frequency discrimination performance. Age alone, i.e., once the effect of subcortical neural synchrony measures or absolute thresholds had been partialed out, did not contribute to frequency discrimination. Overall, the results suggest that frequency discrimination of pure tones may depend both on phase locking precision and on separate mechanisms affected in hearing loss.