Hallucination: Philosophy and Psychology

This new volume of essays, Hallucination: Philosophy and Psychology, is an excellent, although challenging, introduction to recent philosophical work on the subject of hallucinations. Edited by Fiona Macpherson, professor of philosophy at the University of Glasgow and codirector of the Centre for the Study of the Senses at the Institute of Philosophy, University of London, and Dimitris Platchias, a teaching fellow in the Department of Philosophy, University of York, the book arose from a conference held on Crete in 2008. Although it includes a few scientific papers dealing with the neuroimaging and neuropsychology of some hallucinatory experiences, most of the book is philosophy, and it is philosophy that is dense, closely reasoned, up to date, and of a very high caliber.

The often disabling, frequently frightening, and ultimately puzzling phenomenon of hallucinations has interested and stimulated the thinking of psychiatrists for centuries. They have had a similar hold on philosophers, perhaps most famously Descartes. Descartes, it may be said, initiated modern philosophy when his meditations seemed to show that an “evil demon” could have deceived him into believing that what he took to be perceptions of reality were actually hallucinations, a thought which led him to conclude that cogito ergo sum, or, as the philosopher Fiona Macpherson suggests, he is conscious, therefore he exists. From this a world of philosophy was born.

Despite their sharing a common interest, however, psychiatrists rarely consult philosophers for help or guidance in treating patients who say they hear voices, see visions, or feel presences that other people do not. (Philosophical treatments of hallucination are rarely clinically informed, either.) Yet it may be worthwhile for psychiatric clinicians and researchers to familiarize themselves with philosophical “treatments” of these experiences because, in fact, any encounter with someone who reports having hallucinations is puzzling and challenging to the clinician, in part precisely because there are numerous philosophical problems raised in and by having such encounters.

For example, when a patient reports that he or she hears voices talking to or about the patient, how should the clinician interpret this? If this seems an odd question, perhaps because we seem to know what the patient means and it seems unthinkable to doubt the patient’s honest report, it may help to consider that there are several ways of understanding what the patient might be experiencing. For example, as human beings, we sometimes think we hear a voice—someone calling our name, for example—and then realize we haven’t. So we do distinguish, at least at times, perceiving from thinking or believing that we are perceiving. It also seems possible that when a patient reports hearing voices, he or she is actually monitoring the source of normal, inner speech incorrectly—attributing to someone “outside” what actually arises within. Normal inner speech might be amplified in some way, or its normal suppression inhibited, to contribute to such an error. Hallucinations might be memories or images of traumatic events. Hallucinations might be any or all of these things and might all be honestly reported as hearing voices or having hallucinations.

Another set of philosophical questions concerns the possible relationships between hallucinations and states of the brain. It seems unarguable that hallucinations arise from disorders of brain functioning but even this most natural assumption can raise philosophical puzzles. For example, if hallucinations and veridical perceptions (of ordinary, external reality) share common neural pathways in the brain, how can we distinguish them, either introspectively or conceptually? If the brain is a kind of generator of experiences (hallucinated or veridical), one might wonder how perceptual experiences (like voices or visions) arise from or are had by something as seemingly inert as a brain. And if experiences, including hallucinations, somehow arise from neural processes, this does not explain how they represent, refer to, or provide the kind of direct awareness of the items in our environment that they seem to. (There are, after all, no colors in the brain.) In response to these problems, some have suggested that, rather than conceiving of the brain as a kind of generator, it should be thought of as a kind of receiver (for sounds) or lens (for images). Then the brain would not be a source of perceptual experiences but an instrument for having them. In that case, a hallucination might not be a perceptual experience at all (a lens or a recorder does not experience anything), but a kind of trick played on the brain to convince it that it is in a state that it normally occupies when it does perceive (hear or see) something.

The volume addresses some of the fundamental problems that the puzzles of hallucination seem to pose. Are hallucinations the same type of thing as veridical perceptions (arising at the end of the same neuronal pathways, the common kind theory), or are they fundamentally different (perception necessarily implying awareness of the external world, hallucination as if perceiving, but not involving perceptual experience at all, the disjunctive theory)? If there are multiple possible ways in which hallucinations might come about, multiple kinds of thing they might be, how can we distinguish among them? Will neuroimaging or neuropsychology solve the problem? (For example, will documenting activation of the auditory cortex prove that hallucinations are actually heard? Not necessarily, argues Macpherson, since that could also occur in the tricked-brain case, as if in a state of perceiving.) What might it mean to say that hallucinations are introspectively indistinguishable from veridical perceptions and, if they are, how do we tell them apart? How can we account for perceptions seeming to provide valid reasons for belief (seeing is believing), and what does that imply about the reason or rationality of someone who hallucinates and believes what he or she sees or hears?

For psychiatrists who are interested in philosophical treatments of their subject, this book offers the pleasures of concentrated, unstinting, and rigorous philosophical analysis. For others, it is an introduction to be sampled, or a reference to be consulted as needed. Any psychiatrist will encounter philosophical issues when he or she sees patients who report having hallucinations. This book, although it rarely mentions treatment, gives us license and some tools to approach such issues more thoughtfully.