Based on recent insight into the thalamocortical system and its role in perception and conscious experience, a unified pathophysiological framework for hallucinations in neurological and psychiatric conditions is proposed, which integrates previously unrelated neurobiological and psychological findings. Gamma-frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in networks of thalamocortical circuits, thereby transiently forming assemblies of coherent gamma oscillations under constraints of afferent sensory input and prefrontal attentional mechanisms. If perception is (...) based on synchronisation of intrinsic gamma activity in the thalamocortical system, then sensory input to specific thalamic nuclei may merely play a constraining role. Hallucinations can be regarded as underconstrained perceptions that arise when the impact of sensory input on activation of thalamocortical circuits and synchronisation of thalamocortical gamma activity is reduced. In conditions that are accompanied by hallucinations, factors such as cortical hyperexcitability, cortical attentional mechanisms, hyperarousal, increased noise in specific thalamic nuclei, and random sensory input to specific thalamic nuclei may, to a varying degree, contribute to underconstrained activation of thalamocortical circuits. The reticular thalamic nucleus plays an important role in suppressing random activity of relay cells in specific thalamic nuclei, and its dysfunction may be implicated in the biological vulnerability to hallucinations in schizophrenia. Combined with general activation during cholinergic arousal, this leads to excessive disinhibition in specific thalamic nuclei, which may allow cortical attentional mechanisms to recruit thalamic relay cells into resonant assemblies of gamma oscillations, regardless of their actual sensory input, thereby producing an underconstrained perceptual experience. Key Words: Charles Bonnet syndrome; gamma oscillations; hallucinations; late paraphrenia; Lewy body dementia; perception; schizophrenia; thalamocortical system. (shrink)

What we perceive is the product of an intrinsic process and not part of external physical reality. This notion is consistent with the philosophical position of transcendental idealism but also agrees with physiological findings on the thalamocortical system. -Frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in thalamocortical networks, thereby transiently forming assemblies of coherent oscillations under constraints of sensory input and prefrontal attentional mechanisms. Perception and conscious experience may be (...) based on such assemblies and sensory input to thalamic nuclei plays merely a constraining role in their formation. In schizophrenia, the ability of sensory input to modulate self-organisation of thalamocortical activity may be generally reduced. If during arousal thalamocortical self-organisation is underconstrained by sensory input, then attentional mechanisms alone may determine the content of perception and hallucinations may arise. (shrink)

What we perceive is the product of an intrinsic process and not part of external physical reality. This notion is consistent with the philosophical position of transcendental idealism but also agrees with physiological findings on the thalamocortical system. -Frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in thalamocortical networks, thereby transiently forming assemblies of coherent oscillations under constraints of sensory input and prefrontal attentional mechanisms. Perception and conscious experience may be (...) based on such assemblies and sensory input to thalamic nuclei plays merely a constraining role in their formation. In schizophrenia, the ability of sensory input to modulate self-organisation of thalamocortical activity may be generally reduced. If during arousal thalamocortical self-organisation is underconstrained by sensory input, then attentional mechanisms alone may determine the content of perception and hallucinations may arise. (shrink)

This paper addresses the nature of sensed-presence experiences that are commonplace among the bereaved and occur cross-culturally. Although these experiences are often labelled ‘‘bereavement hallucinations’’, it is unclear what they consist of. Some seem to involve sensory experiences in one or more modalities, while others involve a non-specificfeelingorsenseof presence. I focus on a puzzle concerning the latter: it is unclear how an experience of someone’s presence could arise without a more specific sensory content. I suggest that at least (...) some of these experiences consist in a dynamic and non-localized experience of significant and salientpossibilities. This can amount to the sense of currentlyrelating toa particular individual and, by implication, a sense of that person’s presence. Where an experience of this kind also includes sensory qualities, they are inessential to the sense of relatedness and perhaps symptomatic of it. (shrink)

When you hallucinate an object, you are not in the normal sort of concurrent causal sensory interaction with that object. It's standardly further inferred that the hallucinated object does not actually exist. But the lack of normal concurrent causal sensory interaction does not imply that there does not exist an object that is hallucinated. It might be a past‐perceived object. In this paper, I argue that this claim holds for at least some interesting cases of hallucination. Hallucinations (...) generated by misleading cues (e.g. ‘seeing’ Kanizsa triangles), hallucinations of Charles Bonnet Syndrome patients, and dreams are experiences of past‐perceived objects. (shrink)

How is it that many schizophrenics identify certain instances of verbal imagery as hallucinatory? Most investigators have assumed that alterations in sensory features of imagery explain this. This approach, however, has not yielded a definitive picture of the nature of verbal hallucinations. An alternative perspective suggests itself if one allows the possibility that the nonself quality of hallucinations is inferred on the basis of the experience of unintendedness that accompanies imagery production. Information-processing models of “intentional” cognitive processes call for (...) abstract planning representations that are linked to goals and beliefs. Unintended actions - and imagery - can reflect planning disruptions whereby cognitive products do not cohere with concurrent goals. A model of schizophrenic speech disorganization is presented that postulates a disturbance of discourse planning. Insofar as verbal imagery can be viewed as inwardly directed speech, a consequence of such planning disturbances could be the production of unintended imagery. This link between the outward disorganization of schizophrenic speech and unintended verbal imagery is statistically supported by comparing the speech behavior of hallucinating and nonhallucinating schizophrenics. Studies of “borderline” hallucinations during normal, “goal-less” relaxation and drowsiness suggest that experiential unintendedness leads to a nonpathological variant of hallucinatory otherness that is correctable upon emerging from such passive cognitive states. This contrasts with the schizophrenic case, where nonconcordance with cognitive goals reinforces the unintendedness of verbal images and sustains the conviction of an external source. This model compares favorably with earlier models of verbal hallucinations and provides further evidence for a language production disorder in many schizophrenics.Short Abstract: How is it that many schizophrenics identify certain instances of verbal imagery as hallucinatory? This paper proposes that the critical feature identifying hallucinations is the experience of unintendedness. This experience is nonpathological during passive conscious states but pathological if occurring during goal-directed cognitive processing. A model of schizophrenic speech disorganization is presented that postulates a disturbance of discourse planning that specifies communicative intentions. These alterations could generate unintended verbal imagery as well. Statistical data are offered to support the model, and relevant empirical studies are reviewed. (shrink)

Perceptual experiences have been construed either as representational mental states—Representationalism—or as direct mental relations to the external world—Disjunctivism. Both conceptions are critical reactions to the so-called ‘Argument from Hallucination’, according to which perceptions cannot be about the external world, since they are subjectively indiscriminable from other, hallucinatory experiences, which are about sense-data ormind-dependent entities. Representationalism agrees that perceptions and hallucinations share their most specific mental kind, but accounts for hallucinations as misrepresentations of the external world. According to Disjunctivism, the (...) phenomenal character of perceptions is exhausted by worldly objects and features, and thus must be different from the phenomenal character of hallucinations. Disjunctivism claims that subjective indiscriminability is not the result of a common experiential ground, but is because of our inability to discriminate, from the inside, hallucinations from perceptions. At first sight, Representationalism is more congenial to the way cognitive science deals with perception. However, empirically oriented revisions of Disjunctivism could be developed and tested by giving a metacognitive account of hallucinations. Two versions of this account can be formulated, depending on whether metacognition is understood as explicit metarepresentation or as implicit monitoring of first-order informational states. The first version faces serious objections, but the second is more promising, as it embodies a more realistic view of perceptual phenomenology as having both sensory and affective aspects. Affectbased phenomenology is constituted by various metacognitive feelings, such as the feeling of being perceptually confronted with the world itself, rather than with pictures or mere representations. (shrink)

In defence of naïve realism, Fish has advocated an eliminativist view of hallucination, according to which hallucinations lack visual phenomenology. Logue, and Dokic and Martin, respectively, have developed the eliminativist view in different manners. Logue claims that hallucination is a non-phenomenal, perceptual representational state. Dokic and Martin maintain that hallucinations consist in the confusion of monitoring mechanisms, which generates an affective feeling in the hallucinating subject. This paper aims to critically examine these views of hallucination. By doing (...) so, I shall point out what theoretical requirements are imposed on naïve realists who characterize hallucinations as non-visual-sensory phenomena. (shrink)

Like dreaming, hallucination has been a formative trope for modern philosophy. The vivid, often tragic, breakdown in the mind’s apparent capacity to disclose reality has long served to support a paradoxical philosophical picture of sensory experience. This picture, which of late has shaped the paradigmatic empirical understanding the senses, displays sensory acts as already complete without the external world; complete in that the direct objects even of veridical sensory acts do not transcend what we could anyway (...) hallucinate. Hallucination is thus the mother of Representationalism, which insists that it is mental intermediaries that make other.. (shrink)

What are hallucinations? A common view in the philosophical literature is that hallucinations are degenerate kinds of perceptual experience. I argue instead that hallucinations are degenerate kinds of sensory imagination. As well as providing a good account of many actual cases of hallucination, the view that hallucination is a kind of imagination represents a promising account of hallucination from the perspective of a disjunctivist theory of perception like naïve realism. This is because it provides a way (...) of giving a positive characterisation of hallucination—rather than characterising hallucinations in negative, relational, terms as mental events that are subjectively indistinguishable from veridical perceptual experiences. (shrink)

Hallucinations are among the most impressive of psychopathological symptoms and may appear in all the sensory modalities. They are the most common symptom in schizophrenia, where patients usually experience auditory hallucinations, often hearing voices which speak to them in direct communication or in the form of running commentary. One of the major research strategies in psychopathology during the last years has become the neuropsychological reconstruction of psychopathological symptoms in order to detect basic “core” deficits of the different symptoms. Given (...) the successful identification of such core deficits, they may then serve as heuristic tools to identify candidate brain regions of putative pathology. These brain sites in turn can be explored with respect to their impact for the pathogenesis of schizophrenia. Among these neuropsychological approaches, one of the most prominent concepts reconstructing schizophrenic symptomatology is the concept of a self-monitoring disturbance, based on the conceptual and empirical work of the group around Christopher Frith. Although this conceptualization is evidence-based and appears plausible, it does not fully explain the high degree of certainty or confidence with which schizophrenic patients usually judge the reality status of their hallucinations and the frequency with which the latter might occur. The concept of self-monitoring disturbance thus provides a necessary but not a sufficient theoretical account of how hallucinations are generated. (shrink)

Synaesthesia is a strange sensory blending: synaesthetes report experiences of colours or tastes associated with particular sounds or words. This volume presents new essays by scientists and philosophers exploring what such cases can tell us about the nature of perception and its boundaries with illusion and imagination.

Previously we reported a three-factor structure for hallucinations accompanying sleep paralysis . These earlier analyses were, however, based on retrospective accounts. In a prospective study, 383 individuals reported individual episodes online providing further evidence for the three-factor structure as well as clearer conceptually meaningful relations among factors than retrospective studies. In addition, reports of individual episodes permitted a more fine-grained analysis of the internal structure of factors to assess predictions based on the hypothesis that a sensed or felt presence is (...) a core experience affecting other SP hallucinations. Results were generally consistent with this hypothesis. In particular, associations among, and temporal stability of, sensory hallucinations were largely explained by their common association with FP. The findings are consistent with REM initiation of a threat activated vigilance system with pervasive effects on the SP experience and suggest a potential model for the thematic organization of nightmares and dreams more generally. (shrink)

There is currently no consensus about a general account of hallucination and its object. The problem of hallucination has de facto generated contrasting accounts of perception, led to opposing epistemic and metaphysical positions, and, most significantly, exposed a manifold of diverging views concerning the intentionality of experience, in general, and perceptual intentionality, in particular. In this article, I aim to clarify the controversial status, experiential possibility, and intentional structure of hallucination qua distinctive phenomenon. The analysis will first (...) detect a phenomenological, Husserlian-informed concept of hallucination in its irreducibility to other kinds and modes of sensory experience. This will set the theoretical basis to develop an account of hallucination by means of a morphological description of those diversified structures of intentional consciousness that lend themselves to generate hallucinatory appearances. I will then describe both the turning of certain kinds of intentional experience into hallucinatory perceptions and the status of hallucinatory objects. This will support the possibility of hallucination in a strict and rigorous sense, elucidate the enigmatic claim that ‘in hallucination we are conscious of something while nothing truly appears,’ and offer a seminal perspective concerning the alleged problem that hallucinations pose on perceptual intentionality. With the aid of some crucial distinctions, I will then argue that hallucinations do not affect perceptual intentionality as a dyadic, relational structure. (shrink)

There are strong resemblances between the neurobiological characteristics of hallucinations occurring in the particular case of schizophrenia and the hallucinatory activity observed during the rapid-eye-movement (dreaming) sleep stage: the same prefrontal dorsolateral deactivation; forebrain disconnectivity and disinhibition; sensory deprivation; and acetylcholine, monoamine, and glutamate modifications.

Hallucinations are among the most impressive of psychopathological symptoms and may appear in all the sensory modalities. They are the most common symptom in schizophrenia, where patients usually experience auditory hallucinations, often hearing voices which speak to them in direct communication or in the form of running commentary. One of the major research strategies in psychopathology during the last years has become the neuropsychological reconstruction of psychopathological symptoms in order to detect basic “core” deficits of the different symptoms. Given (...) the successful identification of such core deficits, they may then serve as heuristic tools to identify candidate brain regions of putative pathology. These brain sites in turn can be explored with respect to their impact for the pathogenesis of schizophrenia. Among these neuropsychological approaches, one of the most prominent concepts reconstructing schizophrenic symptomatology is the concept of a self-monitoring disturbance, based on the conceptual and empirical work of the group around Christopher Frith. Although this conceptualization is evidence-based and appears plausible, it does not fully explain the high degree of certainty or confidence with which schizophrenic patients usually judge the reality status of their hallucinations and the frequency with which the latter might occur. The concept of self-monitoring disturbance thus provides a necessary but not a sufficient theoretical account of how hallucinations are generated. (shrink)

Behrendt & Young (B&Y) suggest that hallucinations occur as a result of decoupling of neuronal populations from sensory control. I propose that such a decoupling is in fact a constant feature of brain activity, even under nonpathological conditions. This position is justified by evidence from recent neurophysiological recording studies. I suggest that hallucinations arise because of a breakdown in segregation of internally and externally generated activity in a neuronal population.

The cholinergic system is a good candidate for the role of determining the relative weight given in cortical information processing to new sensory information versus prior knowledge. We discuss the physiological data supporting this, and suggest that this Bayesian perspective can easily be reconciled with the dynamical framework proposed by Behrendt & Young.

Naïve realists hold that the phenomenology of veridical perceptual experience is in part constituted by environmental objects that the subject is perceiving. Although naïve realism is well-motivated by considering the cognitive and epistemic roles of the phenomenology of veridical perceptual experience, it is considered difficult to explain hallucinatory and imaginative experiences. This paper provides three arguments to address these explanatory problems systematically on behalf of naïve realism. First, I argue that the imagination view of hallucination (IH), which states that (...) hallucinations are involuntary sensory imagination, can be applied to total and neutrally matching hallucinations. Second, I argue for the conjunction of IH and the representational view of imagination (RI), according to which sensory imagination (including hallucination) is representational (shortly RIH). Third, I argue that naïve realism can coherently be integrated with RIH. I finally present an integrative model of perception, imagination and hallucination from the perspective of the combination of naïve realism and RIH. (shrink)

Auditory verbal hallucinations form an essential criterial feature in the schizophrenia definition in the Diagnostic and Statistical Manual of Mental Disorders -IV and International Classification of Diseases -10. In both classificatory systems, the presence of a hallucinatory voice that continuously comments the patient’s behavior or thoughts, or the presence of several voices that discuss the patient with each other, is a sufficient criterion to diagnose schizophrenia. The DSM-IV defines a hallucination as “a sensory perception that has the..

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. Key Words: Blindness; Charles Bonnet; cholinergic; cortical release; delirium; dementia; dream intrusion; hallucination; Perception and Attention Deficit (PAD) model; schizophrenia. (shrink)

The present study attempts to reconstruct Husserl’s account of empirical illusion and hallucination and disclose the significance of sense-deception in Husserl’s phenomenology. By clarifying the relation between the “leibhaftige presence” and “existence” of perceived objects, I shall be able to contend that illusion and hallucination are nullified, invalid perceptions. Non-existence or in-actuality is a form of invalidity: the Ungültigkeit of what demands its insertion in the totality of actual existence. Husserl elaborates an ex-negativo account of in-actuality, in which (...) sensory deception refers to a modal modification, which is always relative and contextual in relation to the total nexus of experience in its intersubjectively validated and harmonious unfolding. (shrink)

Phenomenal character is determined by representational content, which both hallucinatory and veridical experiences can share. But in the case of veridical experience, unlike hallucination, the external objects of experience literally have the properties one is aware of in experience. The representationalist can accept the common factor assumption without having to introduce sensory intermediaries between the mind and the world, thus securing a form of direct realism.

This paper aims at reconciling direct realism on the one hand, that is, the thesis according to which perceptual experiences disclose perceptible facts, with intentionalism, the view that sensory e...

Previous studies have shown that misperceptions and illusory experiences can occur if sensory stimulation is withdrawn or becomes invariant even for short periods of time. Using a perceptual deprivation paradigm, we created a monotonous audiovisual environment and asked participants to verbally report any auditory, visual or body-related phenomena they experienced. The data (analysed using a variant of interpretative phenomenological analysis) revealed two main themes: (1) reported sensory phenomena have different spatial characteristics ranging from simple percepts to the feeling (...) of immersion in a complex multisensory environment and (2) the active contribution of the perceiver where participants report engaging in exploratory processes even when there is nothing to find. Detailed analysis of the qualitative data further showed that participants who reported more perceptual phenomena were more likely to report internal bodily sensations, move more during the experiment and score higher on the Revised Hallucination Scale than those reporting fewer percepts explicitly linking perceptual deprivation to somatic phenomena. The results demonstrate how the variety of sensory experiences induced by perceptual deprivation can give further insight into the factors mediating conscious awareness and may suggest ways in which the brain imposes meaning on the environment under invariant sensory conditions. (shrink)

Sensations can occur in the absence of perception and yet be experienced ‘as if’ seen, heard, tasted, or otherwise perceived. Two concepts used to investigate types of these sensory-like mental phenomena (SLMP) are mental imagery and hallucinations. Mental imagery is used as a concept for investigating those SLMP that merely resemble perception in some way. Meanwhile, the concept of hallucinations is used to investigate those SLMP that are, in some sense, compellingly like perception. This may be a difference of (...) degree. Attempts to reliably differentiate between instances of each type of SLMP remain unresolved. Despite this, the concepts of mental imagery and hallucinations are each routinely used independently of the other. These uses are especially interesting in those published accounts of experiments where equivalent findings about the neuroanatomical correlates of SLMP are reported in support of diverging knowledge-claims about the role of SLMP in neurocognitive processes. This practice presents a puzzle. To examine one aspect of this puzzle, I compare the uses of these two scientific concepts in three ways: examining their roles in differentiating between types of SLMP; exploring how their respective historical developments intersect; and analysing their contributions in neuroimaging experiments. In presenting this series of comparative analyses, I will draw on three themes from historical, philosophical, and social studies of scientific practices: interest in material contributions to knowledge; accounts of how concepts are used in experiments; and explorations of the historical conditions within which current practices emerge. Building on this literature, my comparative analyses supports five related claims. My first claim is that the concepts of mental imagery and hallucinations are each used as independent tools in neuroimaging experiments. My second claim is that, as experimental tools, the concepts of mental imagery and hallucinations are each used for investigating discrete epistemic goals. My third claim is that there are implicit interdependent associations that structure the uses of these two concepts as tools for independently investigating these discrete epistemic goals in neuroimaging experiments. This third claim rests on my analyses of both past and present uses of each concept. Firstly, as seen in their intersecting histories, there are disciplined performances of using the concepts of mental imagery and hallucinations that carry-along shared associations about the mediating role of SLMP in thought. Secondly, these interdependent ‘mediator-view’ associations continue to structure the independent uses of each concept as a tool for investigating SLMP in pursuit of specific goals. Taking this further, my fourth claim is that recognising the structured uses of the concepts of mental imagery and hallucinations can help to account for how equivalent SLMP-neuro-correlates are generated in support of diverging knowledge-claims. Finally, my fifth claim is that the structured uses of these concepts as tools can contribute to experiments in ways analogous to, yet not equivalent with, the active contributions of material instruments. Bringing these claims together, I argue that the concepts of mental imagery and hallucinations operate as structured tools that can actively contribute to the knowledge generated by neuroimaging experiments. In presenting this argument I seek to demonstrate that examining the structured uses of concepts as tools can complement existing approaches to studying how the heterogeneous dynamics of experimental practices can come to contribute to scientific knowledge in unintended ways. (shrink)

Hallucination: Philosophy and Psychology is an edited MIT press collection that contributes to the philosophy of perception. This collection is a significant addition to the literature both for its excellent choice of texts, and its emphasis on the case of hallucinations. Dedicating a volume to hallucinatory phenomena may seem somewhat peculiar for those not entrenched in the analytic philosophy of perception, but it is easy enough to grasp their significance. Theories of perception aim to give a fundamental characterization of (...) perceptual experience, which are experiences with a sensory phenomenal character. Such perceptual experiences include cases of successfully perceiving something, but also some cases of merely seeming to perceive. This is because prima facie, some cases of seeming to perceive are more than merely thinking that one does ; they are cases of misperceiving. Hallucinations are .. (shrink)

Applying Behrendt & Young's (B&Y's) model of thalamocortical synchrony to complex visual hallucinations in neurodegenerative disorders, such as dementia with Lewy bodies and progressive supranuclear palsy, leads us to propose that the primary pathology may be cortical rather than thalamic. Additionally, the extinction of active hallucinations by eye closure challenges their conception of the role of reduced sensory input.

Game Transfer Phenomena refers to a cluster of involuntary phenomena related to playing videogames, including sensory and cognitive intrusions, transient changes in perception and self-agency. The Game Transfer Phenomena Scale has been used to measure the frequency of GTP with respect to five factors. The present study aimed to validate an instrument for assessing the multiple dimensions of GTP that helps clarify the distinction between GTP experiences. GTP were contextualized onto the spectrum of intrusive cognitions, perceptual distortions, and dissociations. (...) The relationship between GTP, involuntary phenomena without game content in terms of, e.g., hallucinations and perceptual distortions, and game-biased perceptions, as well as the positive and negative impact of GTP and level of distress were also examined. The data were collected using a survey. Separate confirmatory factor analyses of the dimensions of “inner intrusions/misperceptions,” “outer intrusions/distortions,” and “dissociations/mix-ups” produced acceptable fit indices. The findings show that phenomena manifesting as internal experiences are more common, while those manifesting as externalized intrusions are less common. Correlations between the GTP dimensions, INVWG, and GBPA, such as the insertion of game elements in thoughts, perceptions, and dreams, supported convergent validity. The correlations between the GTP dimensions and hours played supported criterion validity. Distress was correlated with outer intrusions and dissociations/mix-ups, but not with inner intrusions. Taken together, these results support the validity and reliability of the proposed assessment of GTP constructs. (shrink)

Gamma rhythms are associated with external and internal sensory processing. Within the conceptual framework of “top-down” and “bottom-up” processing, this suggests that gamma represents a format common to both camps. As these oscillations facilitate communication in the temporal domain, they may represent a mechanism by which top-down and bottom-up processing can interact. A breakdown in this interaction may lead to hallucinations.

Hallucinations occur in a wide range of organic and psychological disorders, as well as in a small percentage of the normal population According to usual definitions in psychology and psychiatry, hallucinations are sensory experiences which present things that are not there, but are nonetheless accompanied by a powerful sense of reality. As Richard Bentall puts it, “the illusion of reality ... is the sine qua non of all hallucinatory experiences” (Bentall 1990: 82). The aim of this paper is to (...) find out what lends an experience ‘a sense of reality’: what features are required for an experience to feel ‘real’, in the relevant sense? I will investigate the claim that phenomenological features are largely responsible for a sense of reality, and will find this claim wanting. My suggestion is that a sense of reality is created and sustained by the larger nexus of the subject's beliefs. (shrink)

One might think that the best metaphysical theory of the world includes the existence of other minds and of the physical world, while denying that we can know or be certain that this theory is true. This chapter considers Solipsism as a theory about reality. It examines the Veil of Perception, and then considers a series of direct arguments against the Solipsistic Veil, Phenomenalism, and Solipsism itself. The chapter looks at two obviously inadequate arguments for the Veil, namely, Berkeley's inconceivability (...) argument and the argument from causal mediation. Then, the chapter looks at two much more interesting and important arguments, namely, the argument from hallucination and illusion and the argument from color and other secondary qualities. Besides the Veil of Perception, arguments for Idealism and Solipsism depend on an appeal to Ockham's Razor. These arguments can be taken either as providing additional support for Perceptual Realism or as a defense of Inferred Anti‐Idealism. (shrink)

[Working Draft — Comments are welcome! — March 2024] Reductive strong representationalists accept the Common Kind Thesis about subjectively indistinguishable sensory hallucinations, illusions, and veridical experiences. I show that this doesn’t jibe well with their declared phenomenal externalism and argue that there is no sense in which the phenomenal character of sensory experiences is constituted by the sensible properties represented by these experiences, as representationalists claim. First, I argue that, given general representationalist principles, no instances of a sensible (...) property constitute the phenomenal character of the sensory experience that represents them. Second, I argue that, with two very plausible assumptions in place, no sensible property qua universal can constitute the phenomenal character of experiences either. At the end, I offer an alternative picture that is consistent with a naturalist psychosemantics for sensory experiences without embracing phenomenal externalism. (shrink)

Disjunctivism about perceptual appearances, as I conceive of it, is a theory which seeks to preserve a naïve realist conception of veridical perception in the light of the challenge from the argument from hallucination. The naïve realist claims that some sensory experiences are relations to mind-independent objects. That is to say, taking experiences to be episodes or events, the naïve realist supposes that some such episodes have as constituents mind-independent objects. In turn, the disjunctivist claims that in a (...) case of veridical perception like this very kind of experience that you now have, the experiential episode you enjoy is of a kind which could not be occurring were you having an hallucination. The common strategy of arguments from hallucination set out to show that certain things are true of hallucinations, and hence must be true of perceptions. For example, it is argued that hallucinations must have non-physical objects of awareness, or that such states are not relations to anything at all, but are at best seeming relations to objects. In insisting that veridical perceptual experience is of a distinct kind from hallucination, the disjunctivist denies that any of these conceptions of hallucination challenges our conception of veridical perceptions as relations to mind-independent objects. More specifically, I assume that the disjunctivist advocates naïve realism because they think that this position best articulates how sensory experience seems to us to be just through reflection. If the disjunctivist is correct in this contention, then anyone who accepts the conclusion of the argument from hallucination must also accept that the nature of sensory experience is other than it seems to us to be. In turn, one may complain that any such error theory is liable to lead to sceptical consequences. A Humean scepticism about the senses launches a challenge about our knowledge of the world through questioning the conception we have of what sense experience is, and how it can provide knowledge of the world. (shrink)

I develop a view of perception that does justice to Price's intuition that all sensory experience acquaints us with sensible qualities like colour and shape. Contrary to the received opinion, I argue that we can respect this intuition while insisting that ordinary perception puts us in direct contact with the mind-independent world. In other words, Price's intuition is compatible with naïve realism. Both hallucinations and ordinary perceptions acquaint us with instances of the same kinds of sensible qualities. While the (...) instances in hallucination are mind-dependent, those in veridical perception are not. The latter are ontologically over-determined —they have their existence guaranteed both in virtue of having a material bearer and in virtue of being perceived by a mind. Such over-determined instances are mind-independent—they can continue to exist unperceived, because, in addition to the minds that perceive them, their existence is guaranteed by the material objects that are their bearers. (shrink)

Many philosophers and psychologists have sought to explain experiences of auditory verbal hallucinations and “inserted thoughts” in schizophrenia in terms of a failure on the part of patients to appropriately monitor their own inner speech. These self-monitoring accounts have recently been challenged by some who argue that AVHs are better explained in terms of the spontaneous activation of auditory-verbal representations. This paper defends two kinds of self-monitoring approach against the spontaneous activation account. The defense requires first making some important clarifications (...) concerning what is at issue in the dispute between the two forms of theory. A popular but problematic self-monitoring theory is then contrasted with two more plausible conceptions of what the relevant self-monitoring deficits involve. The first appeals to deficits in the neural mechanisms that normally filter or attenuate sensory signals that are the result of one’s own actions. The second, less familiar, form of self-monitoring approach draws an important analogy between Wernicke’s aphasia and AVHs in schizophrenia. This style of self-monitoring theory pursues possible connections among AVHs, inserted thoughts, and the disorganized speech characteristic formal thought disorder. (shrink)

This paper aims at offering a new disjunctivist solution – anomalous disjunctivism – to the screening-off problem. Anomalous disjunctivism focuses on the necessary causal conditions for perception and hallucination. It argues that the proximate cause is contingent on causing a particular kind of sensory experience that can either be perceptual or hallucinatory. It further shows that the perceived thing is a necessary causal condition for perceptual experience and the failure of perception is a necessary causal condition for the (...) hallucinatory counterpart. It is the case that any account of a hallucinatory experience relies on the nature of hallucination, and, therefore, the anti-naïve realist has to agree that the necessary causal condition matters. As a consequence, whatever account we take for a hallucination, it need not apply to its perceptual counterpart. The screening-off problem, thereby, is dissolved. (shrink)

Hallucinations do not originate in a single region of the brain, the thalamus, and cannot be traced back to a single pathological mechanism. They emerge from the complex interaction of several brain regions, and are not necessarily the result of sensory impairment or the effect of a defective filter. In the case of schizophrenia, hallucinations are accessory symptoms, in Bleuler's sense, and are thus not central to this disorder.

Hallucination lies at an intriguing border between psychiatry and philosophy. Although Behrendt & Young (B&Y) tie their proposal to Kantian transcendental idealism, other philosophical positions are equally consistent. Cognition is underconstrained by reality not only in hallucination but also in autism and dreaming. Sensory underconstraint is insufficient to encompass schizophrenia. There is also a breakdown in integrative capacity on the cognitive side. From a wider clinical perspective than schizophrenia, there can be underconstraint or overconstraint in sensory (...) and cognitive functionalities. (shrink)

Despite the recent surge in research on, and interest in, synesthesia, the mechanism underlying this condition is still unknown. Feedforward mechanisms involving overlapping receptive fields of sensory neurons as well as feedback mechanisms involving a lack of signal disinhibition have been proposed. Here I show that a broad range of studies of developmental synesthesia indicate that the mechanism underlying the phenomenon may involve reinstatement of brain activity in different sensory or cognitive streams in a way that is similar (...) to what happens during memory retrieval of semantically associated items. In the paper’s final sections I look at the relevance of synesthesia research, given the memory model, to our understanding of multisensory perception and common mapping patterns. (shrink)

Examining tensions between the past and present uses of scientific concepts can help clarify their contributions as tools in experimental practices. This point can be illustrated by considering the concepts of mental imagery and hallucinations: despite debates over their respective referential reliabilities remaining unresolved within their interdependent histories, both are used as independently stable concepts in neuroimaging experiments. Building on an account of how these concepts function as tools structured for pursuit of diverging goals in experiments, this paper explores this (...) tension by re-examining the continued reliance of each concept on inverse characterisations inherited from the nominally-discarded ‘mediator-view’ of sensory-like mental phenomena (SLMP). In doing so, I seek to demonstrate how examining unresolved tensions can help highlight that entrenched associations can remain both integral to, and obscured by, the uses of concepts as goal-directed tools within experimental practices. (shrink)

Culture shapes our basic sensory experience of the world. This is particularly striking in the study of religion and psychosis, where we and others have shown that cultural context determines both the structure and content of hallucination-like events. The cultural shaping of hallucinations may provide a rich case-study for linking cultural learning with emerging prediction-based models of perception.

Abstract: How it is that one's own thoughts can seem to be someone else's? After noting some common missteps of other approaches to this puzzle, I develop a novel cognitive solution, drawing on and critiquing theories that understand inserted thoughts and auditory verbal hallucinations in schizophrenia as stemming from mismatches between predicted and actual sensory feedback. Considerable attention is paid to forging links between the first-person phenomenology of thought insertion and the posits (e.g. efference copy, corollary discharge) of current (...) cognitive theories. I show how deficits in the subconscious mechanisms regulating inner speech may lead to a 'fractured phenomenology' responsible for schizophrenic patients' reports of inserted thoughts and auditory verbal hallucinations. Supporting work on virtual environments is discussed, and lessons concerning the fixity of delusional belief are drawn. (shrink)

The philosophy of grief has directed little attention to bereavement’s impact on perceptual experience. However, misperceptions, hallucinations and other anomalous experiences are strikingly common following the death of a loved one. Such experiences range from misperceiving a stranger to be the deceased, to phantom sights, sounds and smells, to nebulous quasi-sensory experiences of the loved one’s presence. This paper draws upon the enactive sensorimotor theory of perception to offer a phenomenologically sensitive and empirically informed account of these experiences. It (...) argues that they can be understood as deriving from disruption to both sensorimotor expectations and perceived opportunities for action, stemming from the upheaval of bereavement. Different facets of the enactive sensorimotor approach can help to explain different types of post-bereavement perceptual experience. Post-bereavement misperceptions can be accounted for through the way that alterations to sensorimotor expectations can result in atypical ‘amodal completion’, while bereavement hallucinations can be understood as ‘appearances’ that fail to form part of the usual patterns of sensorimotor contingency. Quasi-sensory experiences of the presence of the deceased can be understood as resulting from changes to perceived affordances. This paper aims to demonstrate the explanatory value of key aspects of the sensorimotor approach by highlighting how they can help to explain the phenomenology of post-bereavement experiences. However, it also illuminates certain areas in which the sensorimotor approach ought to be supplemented, especially if it is to account for tight connections between perception, affect, and intersubjectivity that are salient in grief. (shrink)

The philosophy of grief has directed little attention to bereavement’s impact on perceptual experience. However, misperceptions, hallucinations and other anomalous experiences are strikingly common following the death of a loved one. Such experiences range from misperceiving a stranger to be the deceased, to phantom sights, sounds and smells, to nebulous quasi-sensory experiences of the loved one’s presence. This paper draws upon the enactive sensorimotor theory of perception to offer a phenomenologically sensitive and empirically informed account of these experiences. It (...) argues that they can be understood as deriving from disruption to both sensorimotor expectations and perceived opportunities for action, stemming from the upheaval of bereavement. Different facets of the enactive sensorimotor approach can help to explain different types of post-bereavement perceptual experience. Post-bereavement misperceptions can be accounted for through the way that alterations to sensorimotor expectations can result in atypical ‘amodal completion’, while bereavement hallucinations can be understood as ‘appearances’ that fail to form part of the usual patterns of sensorimotor contingency. Quasi-sensory experiences of the presence of the deceased can be understood as resulting from changes to perceived affordances. This paper aims to demonstrate the explanatory value of key aspects of the sensorimotor approach by highlighting how they can help to explain the phenomenology of post-bereavement experiences. However, it also illuminates certain areas in which the sensorimotor approach ought to be supplemented, especially if it is to account for tight connections between perception, affect, and intersubjectivity that are salient in grief. (shrink)