Principal investigator: Mattia Riccardi
Funding: Fundação Bial
Hallucinations are a lingering concern for philosophers and psychologists alike. On the one hand, from a philosopher’s viewpoint they represent the paramount case of epistemic disquietude. On the other hand, clinicians and experimental psychologists studying mental disorders often encounter them too. In recent years, however, interest in the problem of hallucinations has become more intense than ever. In philosophy, the recent revival of naïve realism under the label of “disjunctivism” has revitalized the philosophical debate surrounding hallucinations (see , , ). Similarly, the empirical investigation of hallucinations has been an important trend in psychology – in a broad sense – in recent decades . This is largely due to the impressive development of neuro-imaging techniques which have permitted to gather a much deeper insight into the neurobiological underpinnings of such mental phenomena. Unfortunately, philosophers and psychologists concerned with hallucinatory phenomena have rarely shown interest in each other’s work (a rare exception is LarALia10). On the one hand, reference to empirical findings is scarce within the disjunctivism discussion. On the other hand, psychologists give less attention to the conceptual work brought about by philosophers in order to clarify the nature of different kinds of mental events. Accordingly, lack of cross-fertilization between the two areas is the main motivation of this project. Therefore, the general proposal we put forward consists in promoting a multidisciplinary approach to the problem of hallucination as the most appropriate strategy. This key idea will be articulated along three main axes:
- Conceptual puzzles for psychologists: The different theoretical frameworks and methodological approaches adopted in investigating hallucinatory phenomena have made it difficult to provide not only a widely accepted classification (see  for auditory hallucinations), but even a non-contentious definition of them (see , , , ). Furthermore, psychological literature often fails to specify criteria which enable to clearly distinguish hallucinations from other sensory events such as misperceptions, illusions, imagery phenomena and even dreams.
- Empirical puzzles for philosophers: Common to the many versions of disjunctivism that can be found in related literature is the idea that there is a fundamental discontinuity between perceptions and hallucinations: there is no “common factor” which is shared by these two classes of mental phenomena. However, cognitive and neurobiological models typically treat perceptions and hallucinations as being realized in the same functional and anatomical systems. This claim, at least prima facie, contrasts with the discontinuity assumption which is most central to disjunctivism. This tension opens up several questions. How can the view suggested by cognitive and neurobiological models be articulated so as to challenge disjunctivism? And how can disjunctivists defend their core thesis taking into account the functional and anatomical convergence suggested by the neurobiological findings?
- The real puzzle: The phenomenology (phenomenal character) of hallucinatory experience still remains obscure. Particularly puzzling is its “percept-like character” , its misleading “sense of reality” . Sometimes this character is described as “Leibhaftigkeit” , or “vividness”. In the case of veridical perception, vividness is taken to indicate the fact that we are being presented with the objects in our surroundings. For instance, the vividness of my visual experience of my desk is typically the mark of the desk’s presence to me: it is the phenomenal property which gives perception its characteristic “feeling of presence” . Therefore, the challenge presented by hallucination is how to explain vividness without presence.
Overview of the state of the art
- Overview of the philosophical debate: The debate on perception has become increasingly interwoven with the problem of hallucination. Many philosophers have attempted to construe a version of direct realism which is immune to the argument from hallucination. Contributions by philosophers such as Hinton, McDowell, Snowdon and Martin have recently been collated in  and . The key disjunctivist thesis is that an experience is either a veridical perception or a delusional episode. In other words, disjunctivists reject the thesis that delusional experiences and genuine perceptions share a “common factor”, arguing instead that they are two separate classes of mental events.
- Epistemic conception and empirical puzzles: Martin has influentially argued that the only way to describe hallucinations is in terms of their epistemic indiscriminability (EI) from perception (see  and his paper in ). This thesis is also known as the “epistemic conception” (EC) of hallucinations, a version of which is also endorsed by , who argues that hallucinations have the same “cognitive effects” as perceptions. Siegel (see her paper in ) examines, inter alia, how EI might apply to the intuitively plausible case of an hallucinating animal and concludes that EC is not viable. However, only a few contributions take into account empirical research on hallucinations. The most relevant case is , who considers the case of pseudohallucinations and try to extend EC to these phenomena.  and, to a lesser extent, Martin’s paper in  argue against “local supervenience”, i.e. the view that experiential states supervene on patterns of brain activation.
- Overview of the psychological debate: Hallucinations occur in a wide range of pathological conditions: psychiatric disorders, lesion-dependent impairment, degenerative diseases like Parkinson’s or Alzheimer’s (for a survey see , which updates the still-valuable compendium by ). Thus, most experimental work focuses on specific classes of hallucinations (see e.g.  and  for visual as well as  for auditory hallucionations). Particularly relevant for the project are general explanatory models. At the neurocognitive level, most models explain hallucinations as internally produced mental events which occur due to lack of external inhibition; for instance, top-down expectations  or intrinsic thalamocortical activations  which are unconstrained by sensory inputs.  argues that hallucinations result from impairment not only of the perceptual system, but also of attentional mechanisms.  proposes an integration of models based on neural localization and connectivity.
- Conceptual problems: , ,  and  all endorse alternative definitions of hallucinations (see also ). By comparing these proposals, it is possible to individuate the most controversial aspects: What is meant exactly by the claim that no “appropriate” stimulation corresponds to hallucinations? Is lack of insight a defining property?  reviews the problem of classification for the auditory case.
- Vividness: Different explanations have been proposed for hallucinations’ phenomenological vividness.  defends a meta-cognitive account according to which the “sense of reality” in hallucinations is due to inferential error.  challenges inferential explanations by arguing that vividness is a “primitive” phenomenal property, and is thus not judgement-dependent. More recently, inferentialism has been attacked by . In the perceptual case, presence has been explained in terms of acquaintance  and perceptual availability . Relevant to this debate is the cognitive role of attention in perception (, , , ) and in hallucinations (, ) as well that of (working) memory for top-down expectation in perceptual processes (, ).
Research plan and methods
The core idea: multidisciplinarity is the successful methodology. Although philosophers and psychologists have been working intensively in the area of hallucinations in recent years, they have seldom communicated with each other (an important exception is [1/pr]). As we believe this lack of communication to be detrimental to a full understanding of the kind of mental phenomena in question, our proposal consists in a multidisciplinary approach to hallucinations. In other words, the project’s aim is to produce a cross-fertilization between philosophical and psychological investigations of this specific topic. Concretely, the project assumes that (a) philosophical claims about the metaphysical and epistemological status of hallucinations should be systematically tested against the available empirical data and (b) that the psychological investigation of hallucinations should take into account both the conceptual and the phenomenological work provided by philosophers (on phenomenology see again [1/pr]). The project is not experimental, though we believe that it will provide new insights to be tested experimentally in follow-up projects.
Articulating the key idea: the three axis in detail.
The key idea of the project is developed along the three main lines sketched in the summary. In what follows, the three lines are then described in greater detail by illustrating two core problems for each of them that need to be addressed.
- Conceptual puzzles for psychologists:
- Insight (and lack thereof). Is one’s lack of insight into the hallucinatory character of one’s experience a defining feature of hallucinations (see also the problem of the status of pseudohallucinations, point B.1)? Is it possible to arrive at a non-contentious usage of the term? Furthermore, it is important to consider that the lack of insight typical for hallucinations is sui generis: it occurs together with wakefulness (contrary to dreams) and maintained environmental awareness (contrary to imagery).
- Hallucinations and illusions. Illusions are normally conceived of as experiences as of X being F whereby X is not F. Similarly, hallucinations are described as experiences as of X being F whereby there is no X. Consider, however, the standard experimental case in which a subject’s propensity to auditory hallucinations is tested against both a neutral stimulus (noise) and a non-neutral stimulus, such as a
word (see ). The rationale of such an experimental setting would be to study the occurrence of the same phenomenon in the presence of two different types of stimulus. Yet, according to the definitions given above, the first case should be considered a hallucination, and the second an illusion. Furthermore, illusions thus conceived correspond to cases of misperception. Is this claim convincing? How exactly is
perception supposed to go wrong in illusory cases, and how does it differ from the hallucinatory cases? Should illusions simply be positioned somewhere between hallucinations and perceptions ?
- Empirical puzzles for philosophers:
- Indiscriminability and pseudohallucinations. According to disjunctivists (; see also Martin’s paper in ) hallucinations can be characterized only ex negativo, by maintaining that they are subjectively indiscriminable from genuine perceptions (Siegel in  calls this the “epistemic conception”, EC). However, indiscriminability is not a necessary property of empirically-occurring hallucinations. People who hallucinate are often aware that they are experiencing a hallucinaton (such cases are sometimes referred to as pseudohallucinations, see ). Can disjunctivists accommodate EC so as to cover also pseudohallucinatory cases , or should they deny that such cases are genuine hallucinations and thus claim that they raise no philosophical worries? Are these strategies viable at all?
- Partial hallucinations and the “common factor”. In the philosophically paramount case of “complex visual hallucinations”, empirical data suggest that the hallucinated objects typically fill one’s visual field only partially , ). Consider a person who sits in a room and hallucinates a dog sitting on a (real) sofa. Intuitively, this is a case in which one’s experience encompasses existing things (the sofa and the rest of the room) to which one bears a genuine perceptual relation as well as hallucinated things (the dog) to which one bears no perceptual relation. Disjunctivism, however, does not allow perceptions and hallucinations to share any “common factor”: no “merging” is conceivable. How should disjunctivists treat such cases? (see [4/pr])
- The real puzzle:
- At which cognitive level does perceptual vividness emerge? According to one possible answer, it is the result of the judgement we make about the experience we are enjoying . Accordingly, hallucinations are cases of “judgmental error” caused by some metacognitive impairment which prevents a correct discrimination between externally and internally generated experiences. However, the vividness of one’s hallucinatory experience does not seem to depend on one’s cognitive attitude towards it , for one’s judgement on the nature of one’s delusive episode might not affect the episode’s phenomenology. How are we to assess the metacognitive account? Is it viable? Or should we think that vividness is, as it were, a built-in property of hallucinatory experience?
- Accessibility vs. acquaintance. How can we make sense of the very idea of phenomenal presence? Two strategies have been proposed. First,  suggests that presence is to be understood in terms of accessibility or availability (something is present to me if I have perceptual access to it). Second,  explains perceptual presence in terms of our acquaintance with the object presented to us. In general, attention seems to play a fundamental role in our feeling that something is present: the fact that one can track and attend to an object normally counts as a mark of its presence (, , , ). Relevantly,  argues that hallucinatory phenomena are partially due to a deficit in our attentional system. Are availability and acquaintance really promising candidates? And how do they relate to attention? And which kind of attention (stimulus-driven vs. control) is here relevant?
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As alucinações têm sido uma preocupação duradoura quer para filósofos, quer para psicólogos. Por um lado, do ponto de vista do filósofo elas representam o caso mais emblemático de inquietudes epistémicas. Por outro lado, normalmente, a maioria dos psicológicos clínicos e experimentais que estudam desordens mentais confrontam-se com alucinações. Nos últimos anos, porém, o interesse pelo problema das alucinações tornou-se mais intenso que nunca. Em filosofia, o recente renascimento do realismo ingénuo sob a etiqueta “disjuntivismo” revitalizou o debate sobre as alucinações (ver , , ). De forma similar, a investigação empírica das alucinações tem sido uma tendência importante nas várias áreas da psicologia ao longo das duas últimas décadas , sobretudo graças ao impressionante desenvolvimento da técnicas de neuro-imagem, que permitiu ganhar um conhecimento muito mais profundo da base neuro-biológica desses fenómenos mentais. Infelizmente, só raramente filósofos e psicólogos empenhados na investigação dos fenómenos alucinatórios têm mostrado interesse no trabalho recíproco. Por um lado, a referencia a dados empíricos é escassa na discussão sobre o disjuntivismo. Por outro lado, os psicólogos dão pouca atenção ao trabalho conceptual desenvolvido pelos filósofos na tentativa de clarificar a natureza de tipos diferentes de eventos mentais. A falta de fertilização mútua entre as duas áreas é a motivação principal do presente
projeto. Desta forma, a proposta geral aqui avançada consiste na promoção de uma abordagem multidisciplinar como sendo a mais adequada ao problema das alucinações. Esta ideia nuclear é articulada em três eixos principais:
- Problemas conceptuais para psicólogos: Devido aos diferentes paradigmas teóricos e metodológicos adotados na investigação dos fenómenos alucinatórios, tem sido muito difícil fornecer não só uma classificação universalmente aceite (ver  para as alucinações auditivas), mas até uma definição não controversa de tais fenómenos (ver , , , ). Além disso, a literatura psicológica não é capaz, frequentemente, de especificar critérios que permitam distinguir de forma clara as alucinações de outros estados sensoriais tais como percepções erradas, ilusões, fenómenos de imaginação e até sonhos.
- Problemas empíricos para filósofos: Comum às diferentes versões de disjuntivismo que se encontram na literatura é a ideia de que há uma descontinuidade fundamental entre perceções e alucinações: não há nenhum “fator comum” partilhado por estas duas classes de fenómenos mentais. Todavia, normalmente os modelos cognitivos e neuro-biológicos consideram perceções e alucinações como sendo realizadas pelos mesmos sistemas funcionais e anatómicos. Esta tese, pelo menos prima facie, contrasta com a assunção de descontinuidade que é central para o disjuntivismo. Pode a visão sugerida pelos modelos cognitivos e neuro-biológicos ser articulada de forma tal a desafiar o disjuntivismo? E como podem os disjuntivistas defender a sua tese nuclear tendo em conta a convergência funcional e anatómica indicada pelo dados empíricos?
- O problema verdadeiro: a fenomenologia (ou carácter fenomenal) da experiência alucinatória continua obscura. Particularmente enigmático é o seu “caráter percetivo” , o seu enganador “sentido de realidade” . Às vezes, este caráter é descrito em termos de Leibhaftigkeit , ou vividez. No caso das perceções verídicas, a vividez é considerada sinalizar o facto que há objetos presentes no espaço circundante. Por exemplo, a vividez da minha experiência visual da mesa sinaliza, normalmente, a presença da mesa: noutras palavras, é a propriedade fenomenal que confere à perceção a sua característica “sensação de presença” . O desafio da alucinação, porém, é como explicar a vividez sem presença.