Today we present a very special optical illusion: it is called “Fröhlich effect” or “flash-lag effect.” Those who look at the GIF (which you will find by clicking on this link) will observe a red square that advances horizontally when, coming in half, a green square appears for a second.
The green square appears exactly when the red one arrives in the center, but many notice that, in reality, the green square appears late compared to the passage of the “connect.” What’s going on with our brains? The answer is simple, although there are several explanations. These illusions, however, can be understood as a natural consequence of temporal compression in the human visual system.
In other words, when the light of a moving object hits the retina, it takes some time before the object is perceived. In this time frame the object has moved to a new position. This is a hypothesis and is called “the hypothesis of the extrapolation of movement.”
A second explanation is given by the “difference of latency.” According to the latter, the visual system processes moving objects more quickly than flashing objects. This hypothesis of difference in latency states that at the moment when the flashing object is processed, the moving object has already moved to a new position.
You can also explore the flash-lag effect through this website that makes the idea perfectly. What do you see? Is the green square late to the red one? Let us know in the comments below!
About GIF and optical illusions: this moving image is called “The Skipping Pylon” and creates a sort of auditory illusion.