Pinheiro, A. P. | bioRxiv Science

bioRxiv2020

Expectancy changes the self-monitoring of voice identity

Self-voice attribution can become difficult when voice characteristics are ambiguous, and functional magnetic resonance imagines (fMRI) investigations of such ambiguity are sparse. We utilized voice-morphing (self-other) to manipulate (un-)certainty in self-voice attribution in a button-press paradigm. This allowed investigating how levels of self-voice certainty alter brain activation in regions monitoring voice identity areas and unexpected changes in voice playback quality. FMRI results confirm a self-voice suppression effect in the right anterior superior temporal gyrus (aSTG) when self-voice attribution was unambiguous. Although the right inferior frontal gyrus (IFG) was more active during self-generated voice compared to when passively-heard, the putative role of this region in detecting unexpected self-voice changes was not confirmed. Further research on the link between right aSTG and IFG is required and may establish a threshold monitoring voice identity in action. The current results have implications for a better understanding of an altered experience of self-voice feedback leading to auditory verbal hallucinations.

neuroscience↗

bioRxiv2020

Aberrant perceptual judgements on speech-relevant acoustic features in hallucination-prone individuals

Hallucinations constitute an intriguing model of how percepts are generated and how perception can fail. Here, we investigate the hypothesis that an altered perceptual weighting of the spectro-temporal modulations that characterize speech contributes to the emergence of auditory verbal hallucinations. Healthy adults (N=168) varying in their predisposition for hallucinations had to choose the more speech-like of two presented ambiguous sound textures and give a confidence judgement. Using psychophysical reverse correlation, we quantified the contribution of different acoustic features to a listeners perceptual decisions. Higher hallucination proneness covaried with perceptual down-weighting of speech-typical, low-frequency acoustic energy while prioritising high frequencies. Remarkably, higher confidence judgements in single trials depended not only on acoustic evidence but also on an individuals hallucination proneness and schizotypy score. In line with an account of altered perceptual priors and differential weighting of sensory evidence, these results show that hallucination-prone individuals exhibit qualitative and quantitative changes in their perception of the modulations typical for speech. Author summaryHallucinations -- that is, percepts in the absence of an external stimulus -- are prevalent in psychotic disorders such as schizophrenia, but also occur in the general population. To date it is unknown whether the emergence of hallucinations is rooted in an altered perception of sounds. Fusing the psychophysical technique of reverse correlation with concepts from computational psychiatry, this research reveals alterations of sensory processing in hallucination-prone adults. We show that the higher nonclinical adults predisposition to hallucinations, the more they prioritise the sound features atypical for speech such as higher frequencies. At the same time, they express higher confidence in their perceptual judgements. The present approach may contribute to improving early diagnosis and prevention strategies in individuals at risk for psychosis.

neuroscience↗