Studying the nature of hearing imaginary sounds
Researchers say that auditory hallucinations—hearing sounds or voices that aren't really there—are the product of an over-expectant brain.
Hallucinations are a symptom of a number of mental illnesses. 60 to 70% of people with schizophrenia experience hallucinations, and some people with dementia, major depression, and bipolar disorder experience the same things as well. Patients report hearing voices or phantom melodies, though there is growing evidence that people without mental illness hear imaginary sounds as well. Sometimes, drugs, migraines, and lack of sleep can cause hallucinations as well.
Researchers ran an experiment first designed at Yale in the 1890s to test the theory that people hear things that aren't there because they expect to. The idea is that when we hear something, our brain makes sense of what hear by filling in the gaps in what we perceive. Thus, it expects the arrival of certain information. When the brain expects too much, we tend to think that we're perceiving something that we actually are not.
A visual trigger that prompts a Pavlovian reaction
People with mental illnesses aren't the only ones that experience auditory hallucinations. The researchers gathered people who have reported that they regularly hear voices that don't have a discernible source. These people have been diagnosed with having a mental illness, while others were self-declared psychics who have not been diagnosed with any mental illnesses. There was also one control group of people who have not experienced any hallucinations at all. Researchers used forensic psychiatry to vet those who genuinely believed that they were experiencing hallucinations.
The experiment entailed presenting participants with a checkerboard, which functions as a visual stimulus, at the same time as a tone. This tone came at different volumes, and at certain points, the researchers didn't play the tone at all. Participants also underwent brain scans while the experiment was in progress.
The researchers asked the participants to press a button whenever they heard a tone. The participants were asked to press the button longer the more confident they were that they heard the sound. As time went by, the participants began pressing the button whenever they saw the checkerboard, even though they didn't actually hear the tone. According to the findings, all the participants hallucinated hearing the tone, but the effect was more significant in those who had mental illnesses.
The study can give more insight into the nature of mental illness and hallucinations.
Apparently, those with a mental illness also found it more difficult to accept that they did not in fact hear what they thought they heard. The researchers also paid close attention to a region of the brain that facilitates auditory hallucinations when it experiences artificial stimulation. Brain scans show that this region of the brain lit up whenever participants reported hearing a sound that the researchers didn't play. This indicated that the participants truly believed that they were hearing a sound that didn't actually play.
The findings may give more insight into how the brain produces auditory hallucinations. Scientists can find out more about how the experience becomes debilitating for some, but not for others. Researchers can also learn more about how a change in beliefs can facilitate a change in perception.
Get weekly science updates in your inbox!