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Understandings of how visual hallucinations appear have been highly influenced by generative approaches, in particular Friston's Active Inference conceptualization. Their core proposition is that these phenomena occur when hallucinatory expectations outweigh actual sensory data. This imbalance occurs as the brain seeks to minimize informational free energy, a measure of the distance between predicted and actual sensory data in a stationary open system. We review this approach in the light of old and new information on the role of environmental factors in episodic hallucinations. In particular, we highlight the possible relationship of specific visual triggers to the onset and offset of some episodes. We use an analogy from phase transitions in physics to explore factors which might account for intermittent shifts between veridical and hallucinatory vision. In these triggered forms of hallucinations, we suggest that there is a transient disturbance in the normal one-to-one correspondence between a real object and the counterpart perception such that this correspondence becomes between the real object and a hallucination. Generative models propose that a lack of information transfer from the environment to the brain is one of the key features of hallucinations. In contrast, we submit that specific information transfer is required at onset and offset in these cases. We propose that this transient one-to-one correspondence between environment and hallucination is mediated more by aberrant discriminative than by generative inference. Discriminative inference can be conceptualized as a process for maximizing shared information between the environment and perception within a self-organizing nonstationary system. We suggest that generative inference plays the greater role in established hallucinations and in the persistence of individual hallucinatory episodes. We further explore whether thermodynamic free energy may be an additional factor in why hallucinations are temporary. Future empirical research could productively concentrate on three areas. Firstly, subjective perceptual changes and parallel variations in brain function during specific transitions between veridical and hallucinatory vision to inform models of how episodes occur. Secondly, systematic investigation of the links between environment and hallucination episodes to probe the role of information transfer in triggering transitions between veridical and hallucinatory vision. Finally, changes in hallucinatory episodes over time to elucidate the role of learning on phenomenology. These empirical data will allow the potential roles of different forms of inference in the stages of hallucinatory episodes to be elucidated. [ABSTRACT FROM AUTHOR]

Background and purpose: Visual hallucinations are a common, potentially distressing experience of people with Lewy body disease (LBD). The underlying brain changes giving rise to visual hallucinations are not fully understood, although previous models have posited that alterations in the connectivity between brain regions involved in attention and visual processing are critical. Methods: Data from 41 people with LBD and visual hallucinations, 48 with LBD without visual hallucinations and 60 similarly aged healthy comparator participants were used. Connections were investigated between regions in the visual cortex and ventral attention, dorsal attention and default mode networks. Results: Participants with visual hallucinations had worse cognition and motor function than those without visual hallucinations. In those with visual hallucinations, reduced functional connectivity within the ventral attention network and from the visual to default mode network was found. Connectivity strength between the visual and default mode network correlated with the number of correct responses on a pareidolia task, and connectivity within the ventral attention network with visuospatial performance. Conclusions: Our results add to evidence of dysfunctional connectivity in the visual and attentional networks in those with LBD and visual hallucinations. [ABSTRACT FROM AUTHOR]

Objectives: There is a paucity of psychological treatments for visual hallucinations (VH). A key aspect in the psychological treatment of hallucination‐related distress is normalisation to explain that these experiences are commonplace and can be non‐distressing. In order to normalise VH, it is vital that more is known about VH in non‐clinical populations. This study investigated the prevalence, content, context, appraisals, distress, and behavioural reactions to VH in a non‐clinical sample. Design: A cross‐sectional study was conducted. Methods: 466 students completed the Multi‐Modality Unusual Sensory Experiences Questionnaire‐VH subscale with additional contextual follow‐up questions. Results: Of the 466 participants, 395 (84.8%) reported anomalous visual experiences. 176 (37.77%) participants reported VH similar to the content seen in psychosis. Of the overall sample, 17.38% felt their experience met the VH definition. Participants mainly saw figures, when alone and in the evening. Participants endorsed normalising appraisals: 112 out of 176 (78.87%) believed their mind was playing tricks on them and 83 (58.45%) believed they were tired. However, many also believed the VH was a threat to their mental (66, 46.48%) or physical well‐being (41, 28.87%). These negative appraisals were associated with distress. Conclusion: VH are seemingly common in non‐clinical populations and are similar in a number of ways to those of people with psychosis. Awareness that VH occur on a continuum could normalise people's experiences and reduce their negative appraisals and related distress. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.brat.2010.06.003 Byline: Thomas D. Meyer (a), Emma Gudgeon (b), Alan J. Thomas (c), Daniel Collerton (a)(d) Abstract: Depression is common in older people and its identification and treatment has been highlighted as one of the major challenges in an ageing world. Poor physical and cognitive health, bereavement, and prior depression are important risk factors for depression in elderly people. Attributional or cognitive style has been identified as a risk factor for depression in children, adolescents and younger adults but its relevance for depression and mood in elderly people has not been investigated in the context of other risk factors. Author Affiliation: (a) Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK (b) Fleetwood Hospital Lancashire Care NHS Trust, Fleetwood, Lancashire, UK (c) Institute of Ageing and Health, Newcastle University, Newcastle upon Tyne, UK (d) Northumberland, Tyne and Wear NHS Trust, Newcastle upon Tyne, UK Article History: Received 15 March 2009; Revised 23 May 2010; Accepted 4 June 2010

Commentators agree that the Perception and Attention Deficit (PAD) model is a promising model for accounting for recurrent complex visual hallucinations (RCVH) across several disorders, though with varying detailed criticisms. Its central tenets are not modified, but further consideration of generative models of visual processing and the relationship of proto-objects and memory systems allows the PAD model to deal with variations in phenomenology. The commentaries suggest new ways to generate evidence that will test the model.

As many as two million people in the United Kingdom repeatedly see people, animals, and objects that have no objective reality. Hallucinations on the border of sleep, dementing illnesses, delirium, eye disease, and schizophrenia account for 90% of these. The remainder have rarer disorders. We review existing models of recurrent complex visual hallucinations (RCVH) in the awake person, including cortical irritation, cortical hyperexcitability and cortical release, top-down activation, misperception, dream intrusion, and interactive models. We provide evidence that these can neither fully account for the phenomenology of RCVH, nor for variations in the frequency of RCVH in different disorders. We propose a novel Perception and Attention Deficit (PAD) model for RCVH. A combination of impaired attentional binding and poor sensory activation of a correct proto-object, in conjunction with a relatively intact scene representation, bias perception to allow the intrusion of a hallucinatory proto-object into a scene perception. Incorporation of this image into a context-specific hallucinatory scene representation accounts for repetitive hallucinations. We suggest that these impairments are underpinned by disturbances in a lateral frontal cortex-ventral visual stream system. We show how the frequency of RCVH in different diseases is related to the coexistence of attentional and visual perceptual impairments; how attentional and perceptual processes can account for their phenomenology; and that diseases and other states with high rates of RCVH have cholinergic dysfunction in both frontal cortex and the ventral visual stream. Several tests of the model are indicated, together with a number of treatment options that it generates. Keywords: Blindness; Charles Bonnet; cholinergic; cortical release; delirium; dementia; dream intrusion; hallucination; Perception and Attention Deficit (PAD) model; schizophrenia.

Introduction: Hallucinations occur across neurodegenerative disorders, with increasing severity, poorer cognition and impaired hallucination-specific insight associated with worse outcomes and faster disease progression. It remains unclear how changes in cognition, temporal aspects of hallucinations, hallucination-specific insight and distress relate to each other. Methods: Extant samples of patients experiencing visual hallucinations were included in the analyses: Parkinson's Disease (n = 103), Parkinson's Disease Dementia (n = 41), Dementia with Lewy Bodies (n = 27) and Eye Disease (n = 113). We explored the relationship between factors of interest with Spearman's correlations and random-effect linear models. Results: Spearman's correlation analyses at the whole-group level showed that higher hallucination-specific insight was related to higher MMSE score (rs = 0.39, p < 0.001) and less severe hallucinations (rs = −0.28, p <.01). Linear mixed-models controlling for diagnostic group showed that insight was related to higher MMSE (p <.001), to hallucination severity (p = 0.003), and to VH duration (p = 0.04). Interestingly, insight was linked to the distress component but not the frequency component of severity. No significant relationship was found between MMSE and hallucination severity in these analyses. Conclusion: Our findings highlight the importance of hallucination-specific insight, distress and duration across groups. A better understanding of the role these factors play in VH may help with the development of future therapeutic interventions trans-diagnostically. [ABSTRACT FROM AUTHOR]