Are auditory verbal hallucinations related to auditory processing deficits and prosodic impairment in schizophrenia?

© 2015 Dr. Christopher John GrootThe ability to interpret affect and linguistic intent based on the intonation, rhythm, and stress of speech, is known as receptive prosody. As an auditory communicative function, receptive prosody is ultimately reliant on the processing of its constituent perceptual elements, namely, pitch, tone duration, and loudness. Previous research clearly demonstrates that receptive affective prosody is impaired in schizophrenia; however, the findings as regards linguistic prosody are mixed. Similarly, research shows robust impairments for pitch and tone duration processing in schizophrenia samples, yet loudness processing remains relatively unexplored. Recent findings indicates that the pitch and prosodic processing impairments observed in schizophrenia may be linked. Moreover, a small body of recent research suggests a possible relationship between auditory and prosodic impairments, and the experience of auditory verbal hallucination (AVH) in schizophrenia; however, these associations are yet to be thoroughly examined. To this end, this thesis aimed to comprehensively investigate auditory and prosodic processing impairment as a function of the experience of AVH in a schizophrenia patient sample. 15 AVH schizophrenia patients, 15 non-AVH schizophrenia patients and 34 non- psychiatric controls were compared on auditory and prosodic processing tasks, as well as a number of clinical and neurocognitive measures. The auditory processing tasks indexed participants’ sensitivity to differences in the pitch, duration, and loudness of simple tones. The prosodic processing tasks included an affective prosody labeling task, a linguistic prosody labeling task, and a novel affective prosody labeling task comprising speech waveforms that were systematically modulated such that pitch, loudness, or duration cues were singularly available for prosodic decoding. Results indicated that schizophrenia patients had impaired sensitivity to differences in pitch and tone duration but not loudness, when compared with non-psychiatric controls. Overall, AVH schizophrenia patients showed the greatest impairments in tone discrimination when compared with non-psychiatric controls. Schizophrenia patients were also observed to display deficits in prosodic decoding. Again, the AVH schizophrenia patient group showed the largest impairments in affective prosody decoding relative to the non-psychiatric control group. Next, the novel prosody task based on modulated speech waveforms revealed that AVH patients alone were impaired in prosodic decoding based on duration and loudness cues. Moreover, AVH patients but not non-AVH patients were observed to be impaired in decoding interrogative linguistic prosody in speech. Numerous associations between tone discrimination and prosodic decoding were observed within the schizophrenia groups based on percent correct performance data; however, these associations were largely lost when performance was instead measured with a measure of performance that is independent of response bias, namely, d’ (d-prime). The findings from the current study suggest that AVH schizophrenia patients in particular have a profile of noteworthy impairments in auditory and prosodic processing. However, the findings from the modulated affective prosody task and correlational analyses based on d’ data suggest that the relationship between impairments in tone processing and prosodic decoding in schizophrenia may be more subtle and complex than previously suggested