PERCEPTUAL PATHOLOGY AT THE MARGINS OF HALLUCINATION

Dr Ffytche is Reader in Visual Psychiatry at King’s College London, Institute of Psychiatry, Psychology and Neuroscience and Consultant Old Age Psychiatrist at the Maudsley Hospital where he runs a national specialist clinic for visual hallucinations and related symptoms. He has published extensively on clinical and neuroscientific aspects of visual hallucinations and is an international expert on Charles Bonnet Syndrome.Hallucinations - particularly those in the visual modality - are emerging as important symptoms in degenerative brain and eye disease because of their prevalence, clinical impact and implications for future cognitive trajectory. Yet hallucinations are only one of several visual perceptual pathologies that occur in these conditions and the question arises whether experiences traditionally considered distinct from hallucinations - illusions, misperceptions, pareidolias and metamorphopsias, for example - share the pathophysiological mechanism and prognostic implications of hallucinations. Using evidence from Parkinson’s disease, Charles Bonnet Syndrome and different dementias, I will argue that perceptual experiences at the margins of hallucination reflect a range of pathological mechanisms, some shared with hallucinations others not. The findings suggest that closer clinical attention to the phenomenological detail of visual perceptual pathology is required to better predict future outcome and inform treatment decisions.