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Institute of Advanced Study

Dr Bruce K. Christensen

COFUND Senior Research Fellow at College of St Hild and St Bede, (January - March 2016)

Dr Christensen is an Associate Professor in the Research School of Psychology, Australian National University. He is widely recognized among his colleagues in schizophrenia research both for having one of the sharpest and most critical minds in the field, and for possessing highly original insights. He has established a program of research examining the cognitive and neurobiological mechanisms of schizophrenia that is recognized in the field as both rigorous and important. His research has made extremely important contributions to our understanding of anomalous functional brain organization among patients with Schizophrenia and other psychotic disorders.

Auditory hallucinations (AH) are a prominent and debilitating feature of many psychiatric and neurologic conditions. However, they are also surprisingly common in the general population (15% - 20% of healthy individuals experience AH). Some neuroscientific models for such behaviour exist but are poorly understood and not well rooted in behaviour. The research to be undertaken is novel by positing that AH arise from inferential mechanisms built into normal perception. Research has convincingly demonstrated that, while perception feels entirely veridical to the perceiver, it actually fills in many gaps using probabilistic inference. These inferential processes likely realize substantial computational and resource efficiency on the part of the perceiver. The dominant empirical tool for characterizing how perceptual inferences operate is Bayesian estimation, where perception consists of the observer’s registration of sensory events combined with their prior expectations. In this way, AH may arise when prior expectations abnormally guide perception in the context of noisy or fuzzy representations. The current proposal seeks to test this model by studying how people detect voices embedded in acoustic noise. Expectations will be experimentally manipulated by altering the frequency of targets while internal neural noise will be varied by stimulating participants’ auditory cortex with low intensity transcranial magnetic stimulation. Data will be analyzed to ascertain whether false perceptions arise by means of Bayesian estimation.