With the perceived movement into a dark tunnel, viewers expect a change in illumination, so their pupils dilate. In everyday life, your pupils expand and contract without your knowledge, responding to different levels of brightness. In the dark, they dilate to let in more light and allow you to see better. In bright light, they contract so your eyes aren’t overexposed.
Essentially, your brain is constantly trying to anticipate what’s next, using visual cues like color and light intensity, according to the study. For example, moving into a colored space is less problematic than entering a dark, black space, since color still indicates some light by which to see, Laeng explains. But there could be a variety of factors, including past experiences, guiding our perception, according to the study.
“Perhaps the main point is that our oculomotor system controlling the eyes adjust to what we think we see, not what is really out there. In other words, they do not work as a camera, which adjusts according to a photometer, measuring light,” Laeng explains.
Don’t worry if you don’t feel a sense of movement when you stare at these illusions. The study found that these tricks don’t fool all minds. Twenty percent of the 50 study participants who viewed the black hole image didn’t have the sensation that the blackness was expanding, nor did they have a pupilary response, Laeng says. It’s possible that past experiences may influence these viewers to see the image in only two dimensions, the study authors hypothesize. But they don’t really have a specific answer yet for why these disparities exist.
“It was surprising that a sizable minority did not experience the illusion,” Laeng says. “We also did not expect that the difference between the dark holes and the colored ones would be so clear-cut, though we did predict a difference.”
