Schulz-Hildebrandt, Hinnerk
The illusion includes 9 purple dots that are all the same color, but they trick our brain into seeing only the dot we are looking directly at as purple.
A recently developed optical illusion is revealing new information about how the human brain actively constructs colors we see, challenging the idea that color perception is a direct response to light.
Created by biomedical optics engineer Hinnerk Schulz-Hildebrandt, the illusion demonstrates how identical colors can look dramatically different depending on where we focus our gaze.
According to one published in Perception, the illusion features a set of purple dots on a bluish background. Although all the dots are the same color, observers usually they only notice the point they are looking at directly as being truly purple. Surrounding dots appear bluer or even appear to fade, creating a dynamic visual effect that changes as your eyes move.
According to Schulz-Hildebrandt, this phenomenon highlights that the perception of colors is not simply determined by the wavelengths of light, but is shaped by the interaction between the eye and the brain. A key factor lies in the structure of the retina, specifically the distribution of cone cells responsible for color detection, explains .
Humans have three types of cones sensitive to long (red), medium (green/yellow) and short (blue) wavelengths. However, these cells are not evenly distributed. The central part of the retina, known as the fovea, is densely populated with red- and green-sensitive cones, but has very few blue-sensitive cones. This means that the eye is less able to detect blue lightespecially at the direct focus point.
Despite this limitation, the brain normally compensates for these differences, allowing people to perceive colors consistently in everyday life. But in this illusion, this balance is disturbed. As observers focus on a spot, the brain intensifies its “purple intensity” to distinguish it from the background, while nearby spots appear bluer in comparison.
This effect is a example of “simultaneous contrast”a well-known visual phenomenon in which the perception of a color is influenced by surrounding colors. The brain exaggerates differences to make objects stand out more clearly, even if they are physically identical.
The illusion also reflects broader principles observed in viral visual phenomena, such as that of famous blue and black dress and white and gold, in which people perceived the same image in completely different ways.
The researchers say the findings provide valuable information about how visual processing works in real time.
