Are We All Schizophrenic? Part II – Hallucinations

In the last installment of the series, we discovered that delusional thinking is a part of normal life, with an estimate of 1-3% of non-schizophrenic individuals having severe delusional thinking on par with schizophrenia. You might think that hallucinations – the arguably more extreme schizophrenia symptom – would be rarer? You’d be wrong!

Have you ever heard, seen, smelt, felt or tasted something that wasn’t actually there? If you have, you are probably like the overwhelming majority of the world’s population, schizophrenia and psychosis free. Hallucinations, despite common misconceptions, are a part of normal healthy living that most of us put down to a “brain glitch”. Let’s take a look at just how common hallucinating is and how this relates to individuals experiencing schizophrenic hallucinations.

May the destigmitazation commence!

Hallucinations are defined as the perception of an object or event, using any of the five senses (sight, hearing, touch, smell and taste), despite there being no external stimulus. We will leave out hypnagogic (falling asleep) and hypnopompic (waking up) hallucinations, or there we would be no discussion, we would end the debate here by simply stating that we all have the potential to hallucinate practically every day!

For that matter, let’s put sleep deprivation to one side too, as 8 out of 10 of us are likely to have visual hallucinations if sleep deprived for long enough. The longer you go without sleep, the more intense the hallucination. Moreover, forget including childhood in the equation, or bouts of delirious fever.

We should also recognize that even in science research, self-reports of hallucinations are likely under-reported in healthy people for multiple reasons. One reason established by research is an individuals fear of appearing insane. Thankfully, reports of hallucinations are not so easily effected by the need to be socially desirable as reports of delusions are.

A revealing analysis of the World Health Organization’s World Health Survey from 52 countries indicates that the frequency of self-reports of hallucinations in the general population are greatly impacted by culture. For example, estimates of the number of people reporting hallucinations over a 12 month period in Nepal were a hearty 32%. Meanwhile, in Kazakhstan this number was a meagre 0.5%.

While currently there aren’t any real, solid ideas as to why, and more questions being posed than answers being given, let’s put cultural differences aside and take a look at the various forms of hallucinations in a little more detail.

Auditory Hallucinations

“What? Did someone call my name?”

Auditory hallucinations are the most commonly reported type of hallucination in schizophrenia (present in 60-90% of patients) and most commonly manifests as hearing voices, with music hearing also being commonly reported.

One of the largest and most detailed studies on hearing voices estimates that 5-15% of all adults will experience hearing voices at some point during their lifetimes. One percent of these healthy, non-schizophrenic individuals may hear multiple and at times interacting voices with character-like qualities that are typically associated with chronic schizophrenic hallucinations. For many, it’s just a normal mode of experience.

Visual Hallucinations

“I am sure there was a man standing there!”

Visual hallucinations typically involve flashes of light or sightings of people and/or animals and are the second most commonly reported type of hallucination in schizophrenia (16-72% of patients). Let’s not forget that in certain religious circles, seeing a flash of light may be considered a gift or glimpse of God.

Reports estimate that 4-12% of healthy individuals have visual hallucinations (although numbers vary greatly between different countries, as mentioned previously).

Tactile and Somatic Hallucinations

“Ahhhh! Was that a beasty crawling up my leg?!”

Tactile hallucinations involve sensations felt on the skin, like being tapped on the shoulder or an insect crawling along the surface. Somatic hallucinations on the other hand involve more internal physical sensations, like feelings of electricity in the brain or snakes slithering inside the stomach.

One US-based study estimates that tactile and somatic hallucinations occur in around 20% of schizophrenic patients. Currently, how common this is in the general populace is largely unknown. One UK report estimates that 3% of the population experience touch-based hallucinations, 24% of which have no association with poor mental health.

Olfactory and Gustatory Hallucinations

“Can you smell/taste that? No? Just me?”

Olfactory (smell) and gustatory (taste) hallucinations, known as phantosmia and gustatory phantasma respectively, are the least reported hallucinations in schizophrenic patients. This may very well be because they are less distressing and less infamous, but that does not necessarily mean that they are uncommon, and are suspected to be grossly under-reported.

In a US-based study, 17% and 8% of schizophrenic patients experienced olfactory and gustatory hallucinations respectively. Interestingly, initial estimates of hallucinations of smell and taste in the general UK population are pretty similar at 7-8%, with 2-3% of participants having had experienced the hallucinations the month prior to when the study was conducted.

Hallucinations in Schizophrenia

So what is the difference between hallucinations experienced when a person is diagnosed as schizophrenic, compared to when they are diagnosed as mentally healthy? Its worthy of note that not all schizophrenic patients experience hallucinations, with the International Pilot Study of Schizophrenia estimating that approximately 70% of schizophrenic patients experience them. For those that do they are rarely benign or pleasant.

In the schizophrenic population, these hallucinations – that healthy people tend to chalk down to an intriguing blip in reality – are more frequent, intrusive and distressing. The real game-changer is when one believes that these glitches in our naturally skewed, flawed and limited interpretation of reality are real.

Hallucinations as a Sign of Ill-Health?

That being said, there are numerous reports of hallucinations being associated with physical health problems independently of a mental disorder, and those that persist may be worthy of clinical examination. They are often reported in individuals with epilepsy, brain tumors, migraines, visual impairment, stroke, drug withdrawal, sinus diseases, sensory deprivation, narcolepsy, inborn errors of metabolism and various neurodegenerative diseases.

However, an individual that is blessed by never having mental health issues and is in perfect physical health may still experience regular hallucinations. Experiencing hallucinations are far more common than schizophrenia or a related mental disorder, as well as most of the more physical ailments that hallucinations are associated with!

With the misplaced idea that hallucinating is a dead cert sign of mental illness free from your mind, please feel free to share your hallucinatory experiences and let’s see just how common they are.


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Image via ysuel / Shutterstock.


Carla Clark, PhD

Carla Clark, PhD, is BrainBlogger's Lead Editor and Psychology and Psychiatry Section Editor. A scientific consultant, writer, and researcher in a variety of fields including psychology and neuropsychology, as well as biotechnology, molecular biology, and biophysical chemistry, you can follow her on Facebook or Twitter @GeekReports
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