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New Study Shows It's Surprisingly Easy to Make People Have Auditory Hallucinations

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If you’ve ever heard something that wasn't there—an auditory hallucination—you know that the sound seems very, very real. A new study suggests that it's easy to induce auditory hallucinations in people, but it's even easier in people who already claim to hear things that aren't there. The research was published in the journal Science.

Co-author Al Powers is a psychiatric researcher at Yale. Speaking in a study, he said hallucinations “…may arise from an imbalance between our expectations about the environment and the information we get from our senses.”

In other words, he says, "You may perceive what you expect, not what your senses are telling you."

Powers and his colleagues recruited 59 people to help them test that hypothesis. There were four groups of participants: people who heard voices and had been diagnosed with psychosis; people who had been diagnosed with psychosis but didn’t hear voices; people who heard voices but had not been diagnosed with any mental illness (we'll come back to that in a moment); and people who just plain didn't hear voices.

The third group was an unusual one: 15 self-professed psychics. These participants said that they heard voices every day, but unlike people in the first group—those diagnosed with psychosis who heard voices—they weren't bothered by the voices they claimed to hear. In fact, they took them to be communications from supernatural forces or entities.

All the participants then underwent brain scans. While they were in the scanner, the researchers used a combination of sounds and images to trick their brains into producing auditory hallucinations. First, participants were shown a checkerboard and played a sound. Then they were told to listen for the sound. Sometimes it played when the checkerboard appeared. Sometimes it didn't play at all, but the checkerboard showed, which led their brains to expect the sound would be played.

Members of all four groups experienced the hallucinations, hearing noises even in the silence. Their brain scans showed that they really were "hearing" the nonexistent sounds.

Unsurprisingly, the two groups of hallucination-prone people were more susceptible to hearing things. But when they were told that there had in fact been no sound, people with psychosis were less likely to believe it. 

The authors say this difference could potentially help doctors spot, diagnose, and treat psychosis in their patients before it becomes severe.

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science
Geological Map Shows the Massive Reservoir Bubbling Beneath Old Faithful
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Yellowstone National Park is home to rivers, waterfalls, and hot springs, but Old Faithful is easily its most iconic landmark. Every 45 to 125 minutes, visitors gather around the geyser to watch it shoot streams of water reaching up to 100 feet in the air. The punctual show is one of nature’s greatest spectacles, but new research from scientists at the University of Utah suggests that what’s going on at the geyser’s surface is just the tip of the iceberg.

The study, published in the journal Geophysical Research Letters, features a map of the geological plumbing system beneath Old Faithful. Geologists have long known that the eruptions are caused by water heated by volcanic rocks beneath the ground reaching the boiling point and bubbling upwards through cracks in the earth. But the place where this water simmers between appearances has remained mysterious to scientists until now.

Using 133 seismometers scattered around Old Faithful and the surrounding area, the researchers were able to record the tiny tremors caused by pressure build-up in the hydrothermal reservoir. Two weeks of gathering data helped them determine just how large the well is. The team found that the web of cracks and fissures beneath Old Faithful is roughly 650 feet in diameter and capable of holding more than 79 million gallons of water. When the geyser erupts, it releases just 8000 gallons. You can get an idea of how the reservoir fits into the surrounding geology from the diagram below.

Geological map of geyser.
Sin-Mei Wu, University of Utah

After making the surprising discovery, the study authors plan to return to the area when park roads close for the winter to conduct further research. Next time, they hope to get even more detailed images of the volatile geology beneath this popular part of Yellowstone.

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Animals
Why Do Female Spotted Hyenas Give Birth Through Their Pseudo-Penises?
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At the zoo, you can sometimes tell the difference between male and female animals by noting their physical size, their behavior, and yes, their nether regions. Hyenas, however, flip the script: Not only are lady spotted hyenas bigger and meaner than their male counterparts, ruling the pack with an iron paw, they also sport what appear to be penises—shaft, scrotum, and all.

"Appear" is the key word here: These 7-inch-long phalluses don't produce sperm, so they're technically really long clitorises in disguise. But why do female hyenas have them? And do they actually have to (gulp) give birth through them? Wouldn't that hurt … a lot?

The short answers to these questions are, respectively, "We don't know," "Yes," and "OW." Longer answers can be found in this MinuteEarth video, which provides the full lowdown on hyena sex. Don't say we didn't warn you.

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