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Previous investigations found that loudness-contours within individual Mandarin monosyllables can drive categorical perception of Mandarin tone for cochlear implant (CI) users, while in normal hearing (NH) subjects the pitch contour is phonologically acknowledged to be the dominant cue. Here we further examine the weighting strategy of pitch induced and loudness induced contour identification on Mandarin tone perception by CI users. Twenty-seven versions of the disyllabic utterance /Lao3 Shi/ with orthogonally manipulated loudnesscontour and pitch-contour of the voiced portion of the second monosyllable /Shi/ served as the stimuli to both CI and NH subjects. In Mandarin, if /Shi/ is pronounced with high-flatpitched Tone 1 the word means "teacher", with rising Tone 2 it means "well-behaved", or with falling Tone 4 it means "always". CI users generally had poorer word-recognition scores and their inter-subject variance was large. While NH subjects recognized tone reliably based on pitch-contour, half of the CI users relied on pitch-contour, the other half on loudness-contour, implying systematic differences in pitch coding in their CI processing. This paradigm of orthogonal manipulation of pitch and loudness contours could be developed into improved audiometric tests of Mandarin tone perception and pitch coding with CIs.

Detecting patterns, and noticing unexpected pattern changes, in the environment is a vital aspect of sensory processing. Adaptation and prediction error responses are two components of neural processing related to these tasks, and previous studies in the auditory system in rodents show that these two components are partially dissociable in terms of the topography and latency of neural responses to sensory deviants. However, many previous studies have focused on repetitions of single stimuli, such as pure tones, which have limited ecological validity. In this study, we tested whether the auditory cortical activity shows adaptation to repetition of more complex sound patterns (bisyllabic pairs). Specifically, we compared neural responses to violations of sequences based on single stimulus probability only, against responses to more complex violations based on stimulus order. We employed an auditory oddball paradigm and monitored the auditory cortex (ACtx) activity of awake mice (N=8) using wide-field calcium imaging. We found that cortical responses were sensitive both to single stimulus probabilities and to more global stimulus patterns, as mismatch signals were elicited following both substitution deviants and transposition deviants. Notably, A2 area elicited larger mismatch signaling to those deviants than primary ACtx (A1), which suggests a hierarchical gradient of prediction error signaling in the auditory cortex. Such a hierarchical gradient was observed for late but not early peaks of calcium transients to deviants, suggesting that the late part of the deviant response may reflect prediction error signaling in response to more complex sensory pattern violations.

No abstract

Extracting regularities from ongoing stimulus streams to form predictions is crucial for adaptive behavior. Such regularities exist in terms of the content of the stimuli (i.e., what it is) and their timing (i.e., when it will occur), both of which are known to interactively modulate sensory processing. In real-world stimulus streams, regularities also occur contextually - e.g. predictions of individual notes vs. melodic contour in music. However, it is unknown whether the brain integrates predictions in a contextually congruent manner (e.g., if slower when predictions selectively interact with complex what predictions), and whether integrating predictions of simple vs. complex features rely on dissociable neural correlates. To address these questions, our study employed what and when violations at different levels - single tones (elements) vs. tone pairs (chunks) - within the same stimulus stream, while neural activity was recorded using electroencephalogram (EEG) in participants (N=20) performing a repetition detection task. Our results reveal that what and when predictions interactively modulated stimulus-evoked response amplitude in a contextually congruent manner, but that these modulations were shared between contexts in terms of the spatiotemporal distribution of EEG signals. Effective connectivity analysis using dynamic causal modeling showed that the integration of what and when prediction selectively increased connectivity at relatively late cortical processing stages, between the superior temporal gyrus and the fronto-parietal network. Taken together, these results suggest that the brain integrates different predictions with a high degree of contextual specificity, but in a shared and distributed cortical network.