(Roughly) Daily

Still, it’s useful to know the difference… and as Yasemin Saplakoglu explains, that’s a complex process– one that science takes very seriously…

As I sit at my desk typing up this newsletter, I can see a plant to my left, a water bottle to my right and a gorilla sitting across from me. The plant and bottle are real, but the gorilla is a product of my mind — and I intuitively know that this is true. That’s because my brain, like most people’s, has the ability to distinguish reality from imagination. If it didn’t, or if I had a condition that disrupts this distinction, I’d constantly see gorillas and elephants where they don’t exist.

Imagination is sometimes described as perception in reverse. When we look at an object, electromagnetic waves enter the eyes, where they are translated into neural signals that are then sent to the visual cortex at the back of the brain. This process generates an image: “plant.” With imagination, we start with what we want to see, and the brain’s memory and semantic centers send signals to the same brain region: “gorilla.”

In both cases, the visual cortex is activated. Recalling memories can also activate some of the same regions. Yet the brain can clearly distinguish between imagination, perception and memory in most cases (though it is still possible to get confused). How does it keep everything straight?

By probing the differences between these processes, neuroscientists are untangling how the human brain creates our experience. They’re finding that even our perception of reality is in many ways imagined. “Underneath our skull, everything is made up,” Lars Muckli, a professor of visual and cognitive neurosciences at the University of Glasgow, told me. “We entirely construct the world in its richness and detail and color and sound and content and excitement. … It is created by our neurons.”

To distinguish reality and imagination, the brain might have some kind of “reality threshold,” according to one theory. Researchers recently tested this by asking people to imagine specific images against a backdrop — and then secretly projected faint outlines of those images there. Participants typically recognized when they saw a real projection versus their imagined one, and  those who rated images as more vivid were also more likely to identify them as real. The study suggested that when processing images, the brain might make a judgment on reality based on signal strength. If the signal is weak, the brain takes it for imagination. If it’s strong, the brain deems it real. “The brain has this really careful balancing act that it has to perform,” Thomas Naselaris, a neuroscientist at the University of Minnesota, told me. “In some sense it is going to interpret mental imagery as literally as it does visual imagery.”

Although recalling memories is a creative and imaginative process, it activates the visual cortex as if we were seeing. “It started to raise the question of whether a memory representation is actually different from a perceptual representation at all,” Sam Ling, a neuroscientist at Boston University, told me. A recent study looked to identify how memories and perceptions are constructed differently at the neurobiological level. When we perceive something, visual cues undergo layers of processing in the visual cortex that increase in complexity. Neurons in earlier parts of this process fire more precisely than those that get involved later. In the study, researchers found that during memory recall, neurons fired in a much blurrier way through all the layers. That might explain why our memories aren’t often as crisp as what we’re seeing in front of us…

“How Do Brains Tell Reality From Imagination?” from @yaseminsaplakoglu.bsky.social in @quantamagazine.bsky.social.

* Jean-Jacques Rousseau

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As we parse perception, we might send mindful birthday greetings to a man whose work figures into the history of science’s struggle on this issue, Franz Brentano; he was born on this date in 1838. A philosopher and psychologist, his 1874 Psychology from an Empirical Standpoint, considered his magnum opus and is credited with having reintroduced the medieval scholastic concept of intentionality into contemporary philosophy and psychology.

Brentano also studied perception, with conclusions that prefigure the discussion above…

He is also well known for claiming that Wahrnehmung ist Falschnehmung (‘perception is misconception’) that is to say perception is erroneous. In fact he maintained that external, sensory perception could not tell us anything about the de facto existence of the perceived world, which could simply be illusion. However, we can be absolutely sure of our internal perception. When I hear a tone, I cannot be completely sure that there is a tone in the real world, but I am absolutely certain that I do hear. This awareness, of the fact that I hear, is called internal perception. External perception, sensory perception, can only yield hypotheses about the perceived world, but not truth. Hence he and many of his pupils (in particular Carl Stumpf and Edmund Husserl) thought that the natural sciences could only yield hypotheses and never universal, absolute truths as in pure logic or mathematics.

However, in a reprinting of his Psychologie vom Empirischen Standpunkte (Psychology from an Empirical Standpoint), he recanted this previous view. He attempted to do so without reworking the previous arguments within that work, but it has been said that he was wholly unsuccessful. The new view states that when we hear a sound, we hear something from the external world; there are no physical phenomena of internal perception… – source

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