“Do I see ghosts?” (“Zie ik spoken?”) – under this motto Dutch psychologists called around Masha MJ Linszen from the University of Utrecht took part in an online survey a few years ago. We were looking for people who had already experienced hallucinations – that is, had heard, seen, felt or smelled things that were not really there.
Among other things, the team wanted to generate public awareness of such hallucinations, which are often associated with psychiatric or neurological diseases. The phenomenon is not that rare and also affects healthy people, the researchers write in a recent publication in the specialist journal “Schizophrenia”. Studyfor which they evaluated the collected data: An estimated six to 15 percent of the population may experience such a misperception from time to time.
The interest in the survey, which brought to light different manifestations of the phenomenon and differences to pathological forms, was correspondingly lively. From September 2016 to May 2017, more than 10,400 people (almost 70 percent were women) aged 14 to 88 took part.
Common phenomenon
80 percent of the participants had experienced a hallucination at least once in their lives, half in the past month and a third in the previous week. Of course, one cannot draw any conclusions about the general population from this, the authors emphasize. The sample was not representative and it is more likely that people who had experienced hallucinations reacted. Nevertheless, the evaluation provided new insights into the nature of misperceptions.
According to this, acoustic hallucinations are the most common: One third had experienced one in the past month. A good fifth reported optical misperceptions, a little less felt and smelled. Psychologists were somewhat amazed at how many reports resembled pathological forms of hallucinations, such as from people suffering from schizophrenia or drug abusers. For example, many had experienced multi-sensory hallucinations, which is typical of neurological disorders.
voices and shadows
The authors of the study write that it is particularly noteworthy how varied hallucinations can be. The most common auditory hallucinations are voices: some hear their own name, others an unintelligible whisper, or children crying. But music and telephone ring tones were also often mentioned. Shadows top the list of optical misperceptions. With the felt there are different touches, e.g. B. a hand on the shoulder, or a crawling insect. The smell of fire was the most common among the olfactory hallucinations; supposed smells of food, perfume and flowers are also quite common.
The hallucinations were experienced quite differently by the participants, sometimes they lasted just a moment or a few seconds, others reported misperceptions lasting minutes. The experiences were mostly unpleasant, and for some even very stressful, the researchers write. This fits with the idea that there is a whole spectrum of psychotic symptoms: from individual short experiences to a pronounced psychosis.
Lightning-fast processing
The hallucinations are usually explained by the way our brain works: On the one hand, sensory impressions are processed, on the other hand, assumptions are made about what is seen or heard, which can lead to false conclusions, the work says. According to this theory, hallucinations occur more often when the data is bad, such as when it is dusk.
The lightning-fast top-down assumptions make a lot of sense from an evolutionary point of view, and the authors emphasize that they can save your life in an emergency. This could also explain why most hallucinations fall into the “warning signal” category: e.g. B. threatening voices and footsteps, crying children and the smell of fire or gas. However, the evaluation also shows that hallucinations do not necessarily have to be stressful. Overall, they are probably more common or much more “normal” than is often assumed.