Perception is the process by which living beings capture information from the environment in order to process it and acquire knowledge about it, being able to adapt to the situations we experience.
However, in many cases, whether there is a mental disorder or not, perceptions occur that do not correspond to reality, and these perceptual alterations can be grouped into distortions or deceptions, mainly.
While in perceptual distortions a real stimulus is perceived anomalously, in perceptual deceptions there is no stimulus that triggers the perceptual process. The clearest example of this last type of perceptual alteration is hallucinations..
The concept we just mentioned, hallucinationhas been evolving 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 triggering stimulusthe sufferer having the feeling that it is real and that it occurs without the subject being able to control it (this characteristic being shared with obsessions, delusions and some illusions).
Although they are generally indicators of a mental disorder (being a diagnostic criterion of schizophrenia and may appear in other disorders, such as during manic episodes or during depression), hallucinations can also appear in many other cases, such as neurological disorders, drug use, of substances, epilepsy, tumors and even in non-pathological situations of high anxiety or stress (in the form of a nervous paroxysm due to the object of our anxiety, for example).
An example of hallucination
Let’s see below an example that helps us understand what a hallucination is.
“A young man arrives at 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 every time he looks in the mirror he hears a voice talking to him, insulting him, saying no. will come to nothing in life and stating 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 (looking in the mirror). The young man has really had that perception, for him it is a very real phenomenon that he cannot 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 appear stands out. Furthermore, not all of them appear under the same conditions, and there are 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 several categories.
1. Visual hallucinations
First of all, you can find the visual hallucinationsperceived 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 different measurements than those that would be perceived if these stimuli were real, being called Lilliputian hallucinations in the case of smaller perceptions and Gulliverian in the case of seeing them enlarged. Among visual hallucinations there 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 common in organic conditions, trauma, and substance abuse, although they also appear in certain mental disorders.
2. Auditory hallucinations
Regarding the auditory hallucinationsin which the perceiver hears something unreal, they 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 speaking about the individual themselves, or imperative hallucinations, in which that the individual hears voices that order him to do or stop doing something. Hallucinations of this sensory modality are the most frequent in mental disordersespecially in paranoid schizophrenia.
3. Hallucinations of taste and smell
Regarding the senses of taste and smell, hallucinations in these senses are rare and are usually related to the consumption of drugs or other substances, in addition to some neurological disorders such as temporal lobe epilepsy, or even tumors. They also appear in schizophrenia, usually related to delusions of poisoning or persecution.
The haptic hallucinations They 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 among them a subtype called dermatozoic delirium stands out in which there is the sensation of having small animals in the body, being typical consumption of substances such as cocaine).
Apart from these, related to the senses, two more subtypes can be identified.
Firstly, kinesthetic or somatic hallucinations, which cause perceived sensations regarding one’s own organs, normally linked to strange delusional processes.
Secondly and finally, kinesthetic or kinesthetic hallucinations refer to sensations of movement of the body itself that are not produced in reality, being typical of Parkinson’s patients and substance abuse.
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 triggered by 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 causes it. An example would be the perception of someone who perceives the tune of the news every time he hears the noise of traffic.
The same phenomenon occurs in reflex hallucinationonly this time the unreal perception occurs in a different sensory modality. This is the case that occurs in the example presented above.
The extracampine hallucination It occurs in cases where the false perception occurs outside the individual’s perceptual field. That is, something is perceived beyond what could be perceived. An example is seeing someone behind a wall, with no other information that could lead one to think of their existence.
Another type of hallucination is the absence of perception of something that exists, called negative hallucination. However, in this case the behavior of the patients is not influenced as if they perceived that there is nothing, so that in many cases it has come to doubt that there is a true lack of perception. An example is the negative autoscopyin which the person does not perceive himself when looking in a mirror.
Finally, it is worth highlighting the existence of pseudohallucinations. These are perceptions with the same characteristics as hallucinations with the exception that the subject is aware that they are unreal elements.
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, various authors have tried to shed light on this type of phenomenon, some of the most accepted being those who consider that the subject who hallucinates 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 perception 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 excess activation due to stress, lack or excess of environmental stimulation, high suggestibility, the presence of expectations regarding what it will be perceived as, among other options.
Another example, focused on auditory hallucinations, is the Hoffman’s theory of subvocalizationwhich indicates that these hallucinations are the subject’s perception of their own subvocal speech (that is, our internal voice) as something foreign to themselves (a theory that has generated therapies to treat auditory hallucinations with some effectiveness). However, 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 incorrectly, as if there were elements that are really there even though our senses seem to indicate otherwise. However, in the case of hallucinations our sensory organs work perfectly, what changes is the way our brain processes information that arrives Typically, this means that our memories mix with sensory data in an anomalous way, linking previously experienced visual stimuli 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 of not receiving data through that sensory pathway 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 “construct” scenes that tell us what is happening around us. Some diseases can trigger hallucinations in an uncontrolled way, but these are part of our daily lives, even if we do not realize it.
