Eyes Perception
Afterimages
An image that stays in your vision after the thing you looked at is gone. Bright things leave a same-colour copy for a moment. Long stares leave a copy in opposite colours.
Everyone
Illusion
The brain constructs something that is not there.
Showing 22 oddities.
This tag marks entries where the brain constructs something that is not actually there. Afterimages, the Troxler effect, and the cutaneous rabbit illusion are all cases where what you perceive does not match what is physically happening.
The tag exists to separate a constructed experience from a real physical event happening in the body. A reader here is often surprised that something they always assumed was simply seeing, or feeling, is partly invented.
This list will tell you exactly where the construction happens and what real signal it is built from. It will not suggest anything is wrong with your senses. Every brain does this constantly, and the entries here are just the cases where the construction is easy to notice.
Spiritual 5Icky 5Not an emergency 21Get it checked 15Try it 67Learnable 18Party trick 19Vestigial 7Genetic 37Sleep 6Illusion 22Childhood 8Debunked myth 11Community 14Famous people 14Record 7
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Brain Perception
Alice in Wonderland syndrome
Objects, body parts, or the whole room suddenly look far too big, far too small, or far away. It mostly happens to children, often during a fever or infection, and it passes on its own. In adults it is usually linked to migraine.
6–7% of teenagers (size distortion)
Brain Perception
Charles Bonnet syndrome
People who lose a lot of their sight often start to see things that are not there: patterns, faces, small people in costume, whole landscapes. They know the images are not real. It is caused by sight loss, not by mental illness.
10–40% of older people with serious sight loss
Brain Perception
Chronostasis
Glance at a clock and the second hand can seem to freeze for a moment before it moves. The brain hides your eye movement and stretches the first thing you see to cover the gap.
Everyone
Nerves Reflex
Cutaneous rabbit illusion
A few quick taps at the wrist followed by taps at the elbow feel like a small animal hopping up the arm. The brain fills in taps between the two spots that never happened.
Felt on 90% of trials in one brain-scan study
Brain Involuntary
Déjà vu
A strong feeling that you have lived the present moment before, even though you know you have not. About two in three people get it. It peaks between the ages of 15 and 25.
About 2 in 3 people
Eyes Perception
Foveal tritanopia
The very centre of your vision cannot see blue. The middle of the fovea has no blue-sensitive cones at all. You never notice, because the brain fills the colour in from the surrounding area.
Everyone
Brain Perception
Ganzfeld effect
Fill your whole field of view with a featureless colour and, after some minutes, your brain may start inventing shapes, lights, and scenes. Two halved ping-pong balls and a lamp are enough to do it at home.
Most people who try it, in lab tests
Brain Perception
Geometric nightmares
A kind of dream, often during fever in childhood, filled with huge or tiny shapes, infinite space, crushing pressure, and dread. The name comes from an online forum, not a medical text, but each piece of it is well known to neuroscience.
Not known
Brain Involuntary
Jamais vu
A familiar word, face or place suddenly feels strange, as if you are meeting it for the first time. It is the opposite of déjà vu, and researchers think it is rarer. In lab studies, more than half of people felt a common word turn strange after copying it about 30 times.
Unknown. Thought to be rarer than déjà vu.
Brain Perception
Meditation body dissolution
During long, still meditation the brain loses track of the edges of the body. The body can feel indistinct or seem to expand into space. Flotation tanks produce the same effect. It is usually harmless.
About 29% of recent meditators
Brain Perception
Motion aftereffect
Watch something move in one direction for about a minute, then look at something still. The still thing appears to drift the opposite way for a few seconds.
Everyone
Brain Sound
Musical ear syndrome
Some people with hearing loss hear clear, complete music that no one is playing. The brain replays stored songs to fill the silence. Most people with it know the music is not real.
3.6% of people sent for a hearing test
Eyes Perception
Palinopsia
An image that keeps appearing after the thing you saw is gone. A faint afterimage after a bright light is normal and harmless. Copies that persist or return later need a doctor.
Not counted in the general population
Brain Involuntary
Phantom phone vibrations
You feel your phone buzz in your pocket, check it, and nothing happened. Most phone users get this. The cause is not known. The brain may misread ordinary sensations as a buzz.
30–89% of phone users
Eyes Involuntary
Phosphenes
The flashes, rings, and patterns of light you see when you rub or press your closed eyes, or after a knock on the head. Pressure on the eye makes the retina fire without any light.
Anyone with a working retina
Nerves Perception
Pinocchio illusion
Vibrate the biceps tendon while a person touches their own nose with their eyes closed, and their nose can feel as if it is growing. It shows how the brain works out where the body parts are.
About 30% of students in one lab test
Brain Perception
Prisoner's cinema
After hours or days in darkness, people start to see light shows: colours, geometric patterns, and sometimes figures or scenes. Prisoners, truck drivers, pilots, and meditators all report it.
77% of sighted people blindfolded for four days
Brain Involuntary
Rubber hand illusion
Stroke a rubber hand and a person's hidden real hand at the same time, and within a minute or two the brain adopts the rubber hand as its own. It shows that your sense of your body is built moment by moment from sight and touch.
60–80% of participants
Brain Perception
Strange-face illusion
Stare at your own face in a mirror in dim light for a few minutes and it starts to distort. Most people see their features warp. Some see a stranger, an animal, or a monster.
66% see their face distort
Eyes Perception
The blind spot
Each eye has a hole in its field of view where the optic nerve leaves the retina. You never notice it, because the brain paints over the gap with whatever surrounds it.
Everyone
Eyes Perception
Troxler effect
When you hold your gaze on one point, things in the edge of your vision fade out and disappear. The brain stops reporting anything that does not change.
Everyone