Cognitive And Perceptual Mechanisms In Clinical And Non Clinical Auditory Hallucinations

[Truncated abstract] Auditory hallucinations (AH) are one of the most persistent, distressing, and functionally disabling symptoms of schizophrenia. Despite significant research into aetiology and treatment, the full picture of the mechanisms involved in these experiences remains unclear. AH also occur relatively frequently in healthy individuals in the general population, supporting a continuum model of psychotic symptoms. However, there have been recent challenges to this view, including evidence of important differences in the phenomenology and cognitive mechanisms in patient and non-patient voice hearers. The overarching goal of this thesis is to advance our understanding of the commonalities and differences in cognitive and perceptual mechanisms underlying clinical and non-clinical AH. One of the core features of AH involves them being experienced as separate from one s own mental processes. These experiences have predominantly been explained by failures of self-recognition, or reality monitoring difficulties; however evidence points to a broader array of context memory impairments in AH. The first part of this thesis sought to explore the exact nature of context memory deficits in clinical and non-clinical AH. By assessing memory binding of voice and location information, the first two experiments revealed that healthy, hallucination-predisposed individuals are not impaired in either automatic or intentional binding of two external, contextual features of information in memory. In order to make firm conclusions about whether context memory impairments are/are not present in non-clinical compared to clinical AH, the third experiment applied an identical word-voice memory binding task in two separate studies of: (1) hallucination-prone individuals, and (2) schizophrenia patients (with and without AH). Analyses revealed no evidence of impaired binding in high hallucination-prone individuals relative to controls. In contrast, compared to controls, individuals with schizophrenia (both with and without AH) had difficulties binding the two stimulus features (remembering who said what ), alongside difficulties remembering individual words and voices. These results suggest that the extent of context memory deficits in schizophrenia is more wide-ranging than simply a deficit in identifying the self as a source of mental events. Poorer memory for these real, external voices and impaired binding of words to voices were also associated with higher ratings of the loudness of hallucinated voices reported by individuals with AH. The findings in the first part of this thesis underscore the importance of voice recognition difficulties in patients with schizophrenia, including a functional link to AH. The second part of this thesis explored the particular contribution of voice identity processing to clinical and non-clinical AH. Two separate experiments were designed using identical methodology, and age appropriate controls, to assess voice identity discrimination in: (1) individuals with schizophrenia (with and without AH), and (2) healthy undergraduates with a tendency to hallucinate. Results revealed atypical processing of resonance, though not pitch-based cues to vocal identity in patients with and without AH, but intact voice identity discrimination in hallucination-predisposed individuals...