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Hallucinations: definition, causes, and symptoms

Hallucinations: definition, causes, and symptoms

June 24, 2021

The perception is the process by which living beings capture the information from the environment in order to process it and acquire knowledge about it, being able to adapt to the situations we live.

However, in many cases, whether or not there is a mental disorder, perceptions that do not correspond to reality occur, and these perceptual alterations can be grouped into distortions or deceptions, mainly.

While in perceptual distortions a real stimulus is anomalously perceived, in perceptual deceptions there is no stimulus that triggers the perceptual process. The clearest example of this last type of perceptual alteration are hallucinations .


Hallucinations: defining the concept

The concept that we just mentioned, hallucination, it has evolved throughout history and its description has been enriched over the years. Hallucination can be considered as a perception that occurs in the absence of a stimulus that triggers it , having who suffers it the sensation that this one is real and that it happens without the subject being able to control it (being this characteristic shared with obsessions, delusions and some illusions).

Although they are generally indicators of mental disorder (being a diagnostic criterion of schizophrenia and being able to appear in other disorders, such as during manic episodes or during depressions), hallucinations can also appear in many other cases, such as neurological disorders, of substances, epilepsy, tumors and even in non-pathological situations of high anxiety or stress (in the form of nervous paroxysm due to the object of our anxiety, for example).


An example of hallucination

Let's see an example below to help us understand what a hallucination is

"A young man comes to a psychologist's office. There, he tells his psychologist that he has come to him because he is very afraid. Initially he is reluctant to talk to the professional, but throughout the interview he confesses that the reason for being in his office is that whenever he looks in the mirror he hears a voice talking to him, insulting him, saying that he does not it will come to nothing in life and manifesting that it should disappear. "

This example is a fictitious case in which the supposed patient has perceived a stimulus that does not really exist from a specific situation (look in the mirror). The young person really has had that perception, being for him a very real phenomenon that he can not direct or control . In this way, we can consider that it has all the aforementioned characteristics.


However, not all hallucinations are always the same. There is a wide variety of typologies and classifications, among which the one that refers to the sensory modality in which they stand out stands out. In addition, not all appear in the same conditions, there being also multiple variants of the hallucinatory experience.

Types of hallucinations according to sensory modality

If we classify the hallucinatory experience according to the sensory modality in which they appear, we can find ourselves with several categories.

1. Visual hallucinations

First of all you can find the visual hallucinations , perceived through the sense of sight. In this case the subject sees something that does not exist in reality. These stimuli can be very simple, such as flashes or lights. However, more complex elements can be seen, such as characters, animated beings or vivid scenes.

It is possible that these elements are visualized with measures different from those that would be perceived to be these real stimuli, being called Lilliputian hallucinations in the case of smaller and gulliverian perceptions in the case of seeing them enlarged. Within the visual hallucinations is also autoscopy, in which a subject sees himself from the outside of his body, in a way similar to that reported by patients with near-death experiences.

Visual hallucinations are especially frequent in organic pictures, trauma and substance use, although they also appear in certain mental disorders.

2. Auditory hallucinations

Regarding auditory hallucinations , in which the perceiver hears something unreal, can be simple noises or elements with complete meaning such as human speech.

The clearest examples are hallucinations in the second person, in which, as in the example described above, a voice speaks to the subject, hallucinations in the third person in which voices are heard that speak of the individual among them or imperative hallucinations, in the that the individual hears voices that command him to do or stop doing something. Hallucinations of this sensory modality are the most frequent in mental disorders , especially in paranoid schizophrenia.

3.Hallucinations of taste and smell

In regard to the senses of taste and smell, hallucinations in these senses are rare and they are usually related to the consumption of drugs or other substances, in addition to some neurological disorders such as temporal lobe epilepsy, or even in tumors. They also appear in schizophrenia, usually related to delusions of poisoning or persecution.

4. Haptic hallucinations

The haptic hallucinations are those that refer to the sense of touch. This typology includes a large number of sensations, such as temperature, pain or tingling (the latter being called paresthesias, and highlighting among them a subtype called dermatozoic delirium in which one has the sensation of having small animals in the body, being typical of consumption of substances such as cocaine).

Apart from these, related to the senses, two more subtypes can be identified.

In the first place the cenesthetic or somatic hallucinations, that cause perceived sensations with respect to the own organs, normally linked with strange delirious processes.

In second and last place the kinesthetic or kinésicas hallucinations refer to sensations of movement of the own body that are not produced in the reality, being typical of the patients of Parkinson and of the consumption of substances.

As already mentioned, regardless of where they are perceived, it is also useful to know how they are perceived. In this sense we find different options.

Different modes of false perception

The so-called functional hallucinations are unleashed in the presence of a stimulus that triggers another, this time hallucinatory, in the same sensory modality. This hallucination occurs, begins and ends at the same time as the stimulus that originates it. An example would be the perception of someone who perceives the tune of the news every time he hears the traffic noise.

The same phenomenon occurs in the hallucination reflects , only that on this occasion the unreal perception occurs in a different sensory modality. This is the case given in the example above.

The extracampina hallucination it occurs in cases in which false perception occurs outside the perceptual field of the individual. That is, something is perceived beyond what could be perceived. An example is to see someone behind a wall, with no other information that could suggest their existence.

Another form of hallucination is the absence of perception of something that exists, called negative hallucination . However in this case the behavior of patients is not influenced as if they perceive that there is nothing, so in many cases it has come to doubt that there is a true lack of perception. An example is the negative autoscopy , in which the person does not perceive himself when looking at himself in a mirror.

Finally, it is worth mentioning the existence of pseudoalucinations . These are perceptions with the same characteristics as hallucinations with the exception that the subject is aware that they are unreal elements.

Why is there a hallucination?

We have been able to see some of the main modalities and types of hallucinations but, Why do they occur?

Although there is no single explanation in this regard, several authors have tried to shed light on this type of phenomenon, some of the most accepted being those that consider that the hallucinating subject mistakenly attributes his internal experiences to external factors .

An example of this is Slade and Bentall's theory of metacognitive discrimination, according to which the hallucinatory phenomenon is based on the inability to distinguish real from imaginary perception. These authors consider that this capacity for distinction, which is created and is possible to modify through learning, may be due to an excess of activation due to stress, lack or excess of environmental stimulation, a high suggestibility, the presence of expectations as regards what is going to be perceived, among other options.

Another example, focused on auditory hallucinations, is the suboffice theory of Hoffman , which indicates that these hallucinations are the subject's perception of subvocal speech itself (that is, our internal voice) as something alien to itself (theory that has generated therapies to treat auditory hallucinations with some effectiveness). Nevertheless, Hoffman considered that this fact was not due to a lack of discrimination, but to the generation of involuntary internal discursive acts.

Thus, hallucinations are ways of "reading" reality erroneously, as if there were elements that are really there although our senses seem to indicate the opposite. However, in the case of hallucinations our sensory organs work perfectly, what changes is the way in which our brain processes information that arrives Normally, this means that our memories are mixed with the sensory data in an anomalous way, uniting visual stimuli experienced previously to what is happening around us.

For example, this is what happens when we spend a lot of time in the dark or blindfolded so that our eyes do not register anything; the brain begins to invent things because of the anomaly that involves not receiving data through that sensory path while awake.

The brain that creates an imaginary environment

The existence of hallucinations reminds us that we do not limit ourselves to recording data about what is happening around us, but that our nervous system has the mechanisms to "build" scenes that tell us what is happening around us. Some diseases can lead to uncontrolled hallucinations, but these are part of our day to day, even if we do not realize it.

Bibliographic references:

  • American Psychiatric Association (2002). DSM-IV-TR. Diagnostic and Statistical Manual of Mental Disorders. Spanish edition. Barcelona: Masson. (Original in English of 2000).
  • Baños, R. and Perpiña, C. (2002). Psychopathological exploration. Madrid: Synthesis.
  • Belloch, A., Baños, R. and Perpiñá, C. (2008) Psychopathology of perception and imagination. In A. Belloch, B. Sandín and F. Ramos (Eds.) Manual of Psychopathology (2nd edition). Vol I. Madrid: McGraw Hill Interamericana.
  • Hoffman, R.E. (1986). Verbal hallucinations and language production processes in schizophrenia. Behavioral and Brain Science, 9, 503-548.
  • Ochoa E. & De la Fuente M.L. (1990). "Psychopathology of Attention, Perception and Consciousness". In Medical Psychology, Psychopathology and Psychiatry, Vol. II. Inter-American Ed. McGraw-Hill. Fuentenebro. Madrid, pp. 489-506.
  • Seva, A. (1979). "Psychopathology of Perception". In: Clinical Psychiatry. Ed. Spaxs. Barcelona, ​​pp 173-180.
  • Santos, J.L. (2012). Psychopathology. CEDE Preparation Manual PIR, 01. CEDE. Madrid.
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Schizophrenia Overview | Clinical Presentation (June 2021).


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