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Few of us go around proudly announcing that we’ve been hallucinating. But many of us have. Estimates put the percentage of individuals in the adult population who hear voices when no one is speaking at around 13 percent. Perhaps more common is the phenomenon of feeling one’s cell phone vibrate, when, in fact, it has not. Evidence suggests that this is quite widespread — 68 percent of subjects in one study reported experiencing “phantom vibrations,” and 13 percent experienced them daily. This cannot be explained by psychosis; only around 1 percent of people are schizophrenic. It's clear that there are many non-psychotic individuals experiencing hallucinations.
What explains this trend? Recent research suggests that the answer has to do with how perception works. Rather than moving about the world passively perceiving things, it seems we actively anticipate incoming sensory evidence on the basis of prior beliefs. Perception is, in part, based on prediction. Hallucinations appear to have something to do with what the perceiver is expecting to happen. Part of the explanation for why you think your phone vibrated may be that you were expecting a text or call.
Support for this view comes from work on induced hallucinations. In one study, subjects were conditioned to expect the pairing of an illuminated bulb and a tone. Then, upon seeing the bulb illuminate, they subsequently reported hearing the tone, even when it was not presented. This was true of subjects across four different groups: voice-hearers with diagnosed psychosis, non-voice-hearers with diagnosed psychosis, voice-hearers with no diagnosis, and non-voice-hearers with no diagnosis. There were some differences between the groups. For example, voice-hearers both with and without diagnoses were more likely to hallucinate a tone and more confident in their hallucinatory perceptions. But subjects in all four groups were induced to hallucinate.
One upshot of this work is that it seems hallucinations are not just the result of a psychotic episode. We might conceive of them in terms of a hierarchy. There are clinical-grade hallucinations, such as clearly hearing the coherent speech of an apparently real being. And then there are increasingly more run-of-the-mill hallucinations, many of which have no connection to drugs or mental illness. This latter sort is widespread in the general population. This poses interesting questions about what causes these hallucinations.
This research would both support and benefit from a change in the way we tend to think about hallucinations. The fact that many of us experience banal hallucinations should induce a reckoning with the usual stigma attached to the phenomenon. If one in eight adults experience hearing voices that aren’t there, perhaps regular folks and medical professionals alike should have more open minds about reporting such experiences and engaging with such reports in a manner that does not immediately pathologize them. This will help subjects wishing to share their experiences feel more comfortable doing so, and it will help researchers in the quest to explain what's going on. Achieving a better understanding of what’s happening in our brains when we hallucinate requires more subjects willing to participate in studies and more researchers willing to study hallucinations outside the rubric of mental illness. Both ends will be served by eliminating the stigma attached to reporting a hallucinatory episode. And with so many of us fishing our phones out of our pockets when they haven't actually vibrated, a bit more open-mindedness shouldn't be too much to ask.
