08. Neuroscience

6 Perceptual Illusions That Have Different Instant Effects

March 4, 2023

Here are 6 illusions that should catch your eye right off-the-bat. They each involve very different perceptual or knowledge-based processes, but are surprisingly effective at showing how we use much more than visual information to make meaning of the world around us.

1. Relative Brightness

This first illusion is a based on a classic in neuroscience. It comes from master illusion-maker Akiyoshi Kitaoka, who has cleverly amplified the effect by moving a grey square across a sheet of paper with a gradient.

In trying to make sense of the stark contrast between left and right, the visual system acts as if the gray square is being moved out of shadow into bright light, and then into dark shadow. For the square to look that shade in bright light, it would have to be quite dark — so the perpetual system infers that it is.

On the flip side, for the square to look that shade in dark shadow, it would have to be very light—so the perceptual system infers that, instead. The human brain does a lot of work behind the scenes to contextualize visual data before it is processed.

2. Scintillating Starburst

This image represents a new class of illusion, which is quite subtle, but reveals how our minds can creatively construct new perceptions out of geometric patterns. Developed through a collaboration between a visual artist and a psychology researcher, it is somewhat poetically titled as the 'Scintillating Starburst'.

If you see fleeting rays emanating from the center that are brighter than the background, then note that your mind has generated these through a form of pattern recognition (there is only a single shade of grey).

It was refined experimentally the old-fashioned way, by having 100 study participants view 162 different versions which varied in shape, complexity, and brightness.

As the psychology researcher explained from the findings,

''..𝗮 𝗹𝗮𝗿𝗴𝗲 𝗻𝘂𝗺𝗯𝗲𝗿 𝗼𝗳 𝗽𝗿𝗼𝗺𝗶𝗻𝗲𝗻𝘁 𝗶𝗻𝘁𝗲𝗿𝘀𝗲𝗰𝘁𝗶𝗼𝗻 𝗽𝗼𝗶𝗻𝘁𝘀 𝗹𝗲𝗮𝗱𝘀 𝘁𝗼 𝘀𝘁𝗿𝗼𝗻𝗴𝗲𝗿 𝗮𝗻𝗱 𝗺𝗼𝗿𝗲 𝘃𝗶𝘃𝗶𝗱 𝗿𝗮𝘆𝘀, 𝗮𝘀 𝘁𝗵𝗲𝗿𝗲 𝗮𝗿𝗲 𝗺𝗼𝗿𝗲 𝗰𝘂𝗲𝘀 𝘁𝗼 𝗶𝗻𝗱𝗶𝗰𝗮𝘁𝗲 𝘁𝗵𝗲 𝗶𝗺𝗽𝗹𝗶𝗲𝗱 𝗹𝗶𝗻𝗲𝘀.''

This research illustrates how the brain 'connects the dots' to create one’s subjective reality, highlighting the constructive nature of perception.

3. Two-Way Train

This simple animated image has a just a low enough frame rate for motion to be processed, while leaving ambiguity about its direction. You will instinctively see it as moving towards, or away.

The interesting part is that for an illusion, it’s one of the easiest to consciously manipulate. With a little bit of focus you can choose which way it goes, and with some practice perceive it as quickly alternating directions.

4. Dual Street

In this image an identical photo of a street is duplicated side-by-side. However, the road on the right appears to be going much more towards the right, and the left heading more straight.

The effect is strong partly because of our knowledge that streets close together don’t run parallel. If you’d never seen a street before, the effect could be negligible.

5. Artistic Trash

Although more art than illusion, this creative concept does however reveal that we are biased towards recognizing 3D forms.

As the shadow only picks up the contour of the trash pile, it comes as a surprise that what seems random, is actually highly ordered.

6. The Muller-Lyer Illusion

This last illusion is another variation on a classic, also adding motion for to emphasize the effect. Even before reading the description, you’ve probably guessed that the blue and red lines are all the same size. This version also adds a strong impression that each horizontal row of lines is moving like a Mexican wave, but literally the only motion is the arrows.

There are many theories about how this works, but no one’s certain which theory is correct. It may be even be a culture-specific phenomenon.

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