Decades later, researchers recorded the voices of hallucinators with psychotic disorders and presented these subjects with electronically distorted copies. They wanted to see if the hallucinators could identify their own distorted voices. In the same vein, researchers have explored using computerized avatars à la Second Life in the past decade to try and help hallucinating psychotics assign their “presumed persecutors” a face to talk to, with the goal of softening the things these voices said to them.

Corlett also pointed me toward sine-wave speech, a particularly stunning example of the way expectation can seem to shape our reality when it comes to language. You can try it yourself: Listen to this sound (don’t turn your volume too loud). Most people will hear an R2-D2-like swell of vocoder-tinged whistling. Next, listen to this recording of a woman saying, “It was a sunny day, and the children were going to the park,” in a soothing, southern English accent. Now try R2-D2 again. Listening to the whistling sine-wave speech, you’ll likely hear a distorted version of the same “sunny day” sentence. And in all likelihood, you won’t be able to un-hear the words in the first recording now.

Hallucinators may have an easier time parsing the R2-D2-like sounds, even before listening to the other recording. In a 2017 study, nonclinical voice hearers were far better at recognizing the presence of a voice in sine-wave speech than their non-voice-hearing counterparts. And as a group, their brains fired along a pattern distinct from those who couldn’t tell that the sine-wave speech was a voice. This example, Corlett says, builds the case that auditory hallucinations are linked to the processes of expectation and prediction.

Still, Fernyhough points out, there are some potential holes in the idea of predictive coding. “Compared to the conventional view of the brain as a device that processes information coming from the environment, predictive coding starts with a different set of assumptions about how the brain makes predictions about what is in the environment and then learns from them,” he said. And that can make it hard to reconcile with other, more established ways of looking at the brain.

How the deaf brain rewires itself to ‘hear’ touch and sight

Corlett, meanwhile, argues that there’s a gap in inner-speech theory. Citing a study in which people rendered mute from birth reported hearing voices in their heads, he says that the phenomenon can’t be completely explained as the brain misreading itself.

Whatever explanations stand the test of time, the stakes of this science are much higher than understanding why many of us imagine text messages. For some people, hallucinations can be more persistent and disturbing. The science of how these hallucinated touches, sounds, and sights manifest in the mind is still unclear. It’s too early to say how much the causes of auditory hallucinations and other kinds might overlap, Fernyhough says. So far, the research has focused on auditory hallucinations. And to many, the need for that work is quite clear. Eleanor Longden, a mental-health researcher and advocate, has publicly recounted how her own auditory hallucinations have shifted between neutral and distressing at different points in her life. She’s made the case that the social stigma and judgment she received from her doctor at the time made them more negative.

“Hallucinations can be very distressing and debilitating. They can also be neutral or positive,” Fernyhough says. “A better understanding of how they occur and how they can be managed could alleviate a great deal of mental distress.”