Stare at the central white dot for one minute and then look away to a blank white wall. What do you see? Most people see the image in red, white and blue. The illusion works because staring at the blue, green and black fatigues cells in our eye (and brain) that are specialised for these colours. When we look at the white wall, other cells which respond to the complementary colours (red, white and blue) are now more active than the fatigued cells and so we experience these new colours in the after-image.
One coloured patch looks orange and the other looks brown but they are, in fact, physically identical colours. That is, each patch reflects exactly the same wavelength of light.
This illusion is created in our brains, not in our eyes. The eye treats the two coloured patches as identical, but the brain created an alternative interpretation of these colors using other information that is available -- such as the pattern of shading on the cube. There is a part of the brain, called V4, that is responsible for our conscious perception of color.
These two bars move together then move apart. But do they collide or pass in the middle?
A sound can alter the way we perceive this visual event, changing our experience from passing to colliding. You can toggle the sound on and off by clicking the blue loudspeaker button to try it yourself.
Go to the Demos page of the website of the Visual & Multisensory Perception Lab of UCLA.
When a single flash is accompanied with two beeps, the single flash is perceived as two flashes.
The illusion is strongest when the flash is in the periphery (i.e. you are looking ahead and the flash is to one side) but it also sometimes works if you are looking directly at it.
Look at this person speaking. What do you hear? "Ba, ba" or "da, da".
Most people hear "da, da".
Now try again with your eyes closed. Are you sure that it isn't "ba, ba"?
In fact, this movie has been edited such that the lip movements are saying "ga, ga" and the sound is actually "ba, ba". But your brain pulls this information together to create a new interpretation that was different for that received by either your sense of hearing or vision, namely "da, da".
The participant (on the left) sees a rubber hand being stroked by the experimenter (on the right) while his/her own hidden hand is simultaneously stroked. After several minutes of stroking the participant may feel that the rubber hand is now part of their body!
When you play this movie you will see a set of animations that were produced from descriptions and drawings of synesthetic experiences triggered by musical notes. The animations were made from five different synesthetes and so each note is played five times, once for each person. Note the wide variety of different experiences. But perhaps you will also notice some common trends too. Does the vision tend to move more in one direction, and do some notes tend to produce darker or larger visual impressions than others?
These animations were created by Samantha Moore