This study examined prosodic SR performance and its association with acoustic features of target speech, explored the neural mechanisms underlying reduced prosodic SR in schizophrenia patients, and tested the association between patients’ prosodic SR deficits and psychiatric symptoms. Schizophrenia patients performed worse in prosodic SR than in HPs. A better prosodic SR was associated with a shorter duration, lower shimmerness (local), and greater ECR accuracy for target sentences. The prosodic SR reduction in schizophrenia patients was related to a profile (a linear combination) of reduced GMV in the temporal, frontal, and lingual cortex, bilateral thalamus, and cerebellum. A happy SR was associated with total, negative, and general symptoms on the PANSS. These findings may improve negative psychiatric symptoms by improving prosodic SR based on cortical plasticity.
We found that almost all negative prosody of the target speech dampened the SR (compared to the neutral SR) in both participant groups, indicating that negative emotions embedded in speech may disturb the processing of speech meaning, making the reduced vocabulary available for thinking processing under noise masking more conspicuous [10, 11]. This might be due to the combined effect of auditory bottom-up and top-down processing. Prosodic cues may help participants follow the target speech. However, the stimuli used in this study were 12-character sentences that required auditory working memory and sustained attention against noise masking. Our results revealed that better SR was related to better ECR accuracy, shorter durations, and less shimmer target sentences. The variation in the SR under different emotional conditions may be due to the combined effect of the three acoustic features of the target sentences. For example, happy sentences had the lowest ECR accuracy; due to their short duration and medium local shimmer, the final happy SR was similar to that of neutral emotions. Moreover, the rate of change in the SR along the SNR was more easily affected by sadness, anger, and fear (relative to neutrality), indicating that participants cannot significantly improve their SR under these emotional conditions as the SNRs increase and maintain low levels of SR at various SNRs.
This study extended previous findings [11, 13, 19] by showing that SCHs showed remarkable deficits in prosodic SR and the rate of change in the SR, independent of prosodic cues within the target speech. Abnormalities in prosodic SR might be due to reduced GMV, especially in the bilateral MTG/ITG, lingual gyrus, and occipital cortex; right STG, left orbital frontal cortex, and postcingulate cortex; bilateral thalamus; and cerebellum. We also found that neutral, happy, and disgusted SR against noise masking was associated with psychiatric symptoms. A happy SR was associated with negative and general symptom dimensions after controlling for age, sex, education, IQ, illness duration, and drug dose. Previous studies have shown that neutral speech-on-speech recognition performance is associated with positive and negative symptoms on the PANSS [10], and this study suggested that involving the happy component in the speech-in-noise task seems to manifest negative and general aspects of the psychiatric symptoms of SCHs.
Happiness conveyed by vocal expressions is characterized by a faster speech rate and higher fundamental frequencies [41, 42]. An ERP study showed that SCHs may have an alteration in the processing of the happy salience of the voice [43]. Moreover, the perception of natural happiness stimuli discriminates significantly between patients with schizophrenia and healthy controls [44], and the difficulty of recognizing happy emotions is associated with the PANSS score [45]. Our study revealed that embedding happy prosody in speech did not affect SR against masking and could be a stable indicator of psychiatric symptoms. Our results supported the view that SCHs have “speech gating” deficits that are associated with psychiatric symptoms [11] and may update the understanding of this theory: happy SR deficits may reflect dysfunction of brain activities underlying the severity of psychiatric symptoms, particularly the negative and general symptom dimensions, which makes a happy SR a potential behaviorally intervention target for improving psychiatric symptoms. The underlying mechanism of the association between a happy SR and psychiatric symptoms needs further investigation.
This study has several limitations. This was a cross-sectional study, and causality could not be inferred among the associations among prosodic SR, GMV, and psychiatric symptoms. Future research examining the associations among the unaffected first-degree relatives of SCH patients may deepen the understanding of this problem. Additionally, this study did not ask the participants to rate the category or intensity of the target emotion, which may help better explain the differences in the SR among emotional conditions. The strength of this study was that we used multivariate to multivariate methods to determine the associations of prosodic SR with GMV, which is in line with the characteristics of multiple-to-multiple relationships between bioindicators and mental symptoms and tolerable to relatively small sample sizes [46–48].
Implications for clinical practice
Patients with schizophrenia exhibit multidimensional impairments in perception, thinking, emotion, and volitional behaviors. Antipsychotic drugs are currently the mainstream biological treatment for schizophrenia, but there are significant individual differences in the response of patients to antipsychotic drugs [1]. Antipsychotics can effectively alleviate positive psychiatric symptoms (such as hallucinations, delusions, agitation, etc.) in some patients [49, 50], but most of these patients have poor adherence to antipsychotic drugs due to tolerance issues or other reasons, leading to recurrent and persistent disease [1, 2]. Approximately 30% of patients, although able to benefit from medication treatment, have limited efficacy and continue to experience varying degrees of psychiatric symptoms; approximately 10–30% of patients are not sensitive to drugs [1, 50]. Therefore, exploring behavioral intervention methods that help improve the psychiatric symptoms and cognitive function of patients with schizophrenia is highly important for caring for patients with schizophrenia. This study revealed that deficits in prosodic speech-in-noise recognition, based on decreases in gray matter volume in the brain regions involved in sensory-motor, speech, and emotion processing, were associated with negative syndrome, poor insight, and emotional disturbances in patients with schizophrenia. The deficits in prosodic speech-in-noise recognition might be an intervenable behavioral target to improve psychiatric symptoms based on neuroplasticity.