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Charles Bonnet Syndrome, Musical Ears, and Normal Hallucinations

by Jonah Queen

In a previous post on this blog, I wrote about the Mad Pride movement, which advocates for the rights of, and the end of stigma against, those diagnosed with psychiatric disorders. I discussed how the lack of a clear distinction between “normal” and “abnormal” psychology even leads some activists to think of these conditions as extreme emotional or sensory experiences rather than illnesses. Mad pride advocates see a trend of increasing medicalization within psychiatry, arguing that feelings and behaviors are too readily classified as pathological. But this concern with over-medicalization is not unique to the Mad Pride movement. It is expressed by a wide range of individuals, including those within the mental health establishment. But there is one area where the field of mental health seems to be moving in the opposite direction: hallucinations. DSM-5, which has been criticized for overly broad definitions of psychiatric disorders, is restricting the diagnostic criteria for schizophrenia, making it so that hearing voices (with no additional symptoms) is no longer sufficient for a diagnosis.

The cover of the report in which Charles Bonnet first described the condition which would be named after him (from

This change is due to current research that shows hallucinations are not always a sign of psychosis and are also surprisingly common (according to some sources, ten percent of the population occasionally hears voices). Doctors, researchers, and patient advocacy groups are working to spread this knowledge and to overcome the belief among the general population that experiencing hallucinations makes someone “crazy.”

A hallucination is defined as a perceptual experience that does not come from an external source. They can be caused by a variety of disorders (whether psychiatric, neurological, or somatic) and can occur in healthy individuals in response to psychotropic drugs (like hallucinogens such as LSD and psilocybin) or stress (including sleep deprivation). But there are many other common phenomena that can also be described as hallucinations, though they might not be thought of as such due to their mundane and unobtrusive nature. These include experiences that many of us have had, such as hearing your name being called, hearing a phone ringing, or feeling your cellphone vibrating in your pocket, even though none of those things are actually occurring. Sometimes these experiences can be caused by our brains misinterpreting real sounds. Hearing a “phantom” phone ring can happen in response to faint background noise in a frequency similar to that of the ring, since it is a sound many of us are (even unconsciously) always listening for. 

But while such mild hallucinations usually do not invoke concern in the one experiencing them or make others question that individual’s mental health, there are other types of hallucinations that do, despite also being fairly common and not considered symptomatic of mental illness. Occasionally people who have lost or are losing one of their senses will experience hallucinations. Those with vision loss can experience bizarre visual hallucinations (referred to as visual release hallucinations or Charles Bonnet syndrome). The hallucinations can take a variety of forms, ranging from abstract shapes and patterns to vivid images of faces, people, animals, and cartoon-like figures, often appearing small in size. A related condition can affect those with impaired hearing. People with acquired hearing loss can experience auditory hallucinations of voices and music (sometimes called musical ear syndrome). The hallucinations are thought to be caused by the release phenomenon, where the absence of sensory stimulation paradoxically leads to the triggering of certain neurons since the neurons that normally inhibit them are no longer being activated. A less extreme version of this phenomenon can cause hallucinations in response to sensory deprivation or even when looking at a blank wall or featureless landscape. Charles Bonnet and musical ear syndrome might also be related to phantom limb syndrome, and, in fact, there exists a “phantom eye syndrome” in which individuals who have had an eye removed feel phantom pain and experience hallucinations, though the hallucinations are somewhat different than those experienced with Charles Bonnet syndrome.

An illustration of a Charles Bonnet syndrome hallucination and the underlying vision loss (from

Patients are usually aware that what they are seeing or hearing are, in fact, hallucinations, but they can still be alarming or disturbing, particularly because they might be mistaken as a sign of developing psychosis or dementia (especially since the types of sensory loss that leads to these hallucinations are more common in the elderly). These phenomena often go unreported, as patients are worried about not being taken seriously or labeled as mentally ill if they tell others. And because of the lack of reporting, many health professionals are unaware of these syndromes, which in turn makes them more likely to be misdiagnosed. Researchers of these conditions emphasize that healthcare workers need to be aware of such hallucinations in order to correctly diagnose the condition and reassure their patients that such phenomena are common in those with sight or hearing loss and not a sign of anything more serious.

The hallucinations that occur in Charles Bonnet syndrome and musical ear syndrome (along with the other types of hallucinations mentioned in this post) are considered non-psychotic hallucinations (and sometimes referred to as pseudohallucinations) because those experiencing them are aware that they are hallucinations rather than accurate perceptions of their surroundings. When someone has difficulty distinguishing their hallucinations from external reality or believes that the hallucinations are being caused by some external force (which can occur in schizophrenia), the hallucinations are considered psychotic hallucinations. 

In some ways this emerging view of hallucinations is in line with the opinions of certain Mad Pride groups, who believe that hallucinations themselves are not a problem, and that difficulties only arise when people are unable to cope with them. But many in the movement would disagree with the distinction between psychotic and non-psychotic hallucinations, since it is still a way to classify people as either “healthy” or “ill.” However, I think that this distinction is important, in part, because of the differences between they types of hallucinations (whether they can be distinguished from reality and how distressing they can be, for example), and also because it leads to a more nuanced (and accurate) discussion of anomalous sensory experiences where continued research will bring new insights into human perception and the debates about mental health.

Want to cite this post?

Queen, J. (2015). Charles Bonnet syndrome, musical ears, and normal hallucinations. The Neuroethics Blog. Retrieved on , from


  1. Jonah- very interesting stuff, I especially liked the discussion of mundane hallucinations. Question on the pathological/natural division- could that broad division perhaps be hiding the sorts of nuanced description you are after? Specifically- the suggestion you imply here is that pathological hallucinations include both distressing hallucinations (defined by their affect) and those that cannot be distinguished from reality (defined by their convincing-ness). The only unifying feature there seems to be the pathology- the fact that both of those types of hallucinations could impede operating in the world- rather than some common structure. Of course, that is speculation, but the basic idea there is that for this case the pathological distinction could easily be replaced with a less normative one, without loss of nuance or accuracy.


  2. Okay, not exactly the most relevant but still generally on topic: hallucinations are so common place, even (somewhat neuro-inspired) deep learning software (originally designed for image classification) can be made to hallucinate!


  3. Thanks Riley, and I'm sorry for the late reply. I agree with you that impeding function and ability should be the primary trait for classifying symptoms as pathological. And psychiatry seems to be moving in that direction as well. (That's also why I'm a bit more critical of the Mad Pride movement than might come across in my posts, since the idea that symptoms of mental illness are only a problem if they negatively impact one's life, is fairly mainstream now).

    What I find interesting about CBS is that it blurs some of the boundaries of these definitions. It is a neurological condition caused by a non-neural injury or illness that mimics a psychiatric disorder. And also, though I might not have been clear about this in the post, knowledge of the disorder is not always enough to prevent distress in those who have it.

    And I've heard about Google deep dream software, but never thought about it hallucinating. That's pretty cool.


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