Check out these mysterious optical illusions that affect our visual perception.
- Troxler's effect or "fading" causes images to disappear from your field of vision.
- Scientists don't have a full understanding yet of how this works.
- The effect is linked to the way neurons are adapted by the visual system.
Why do we some times see things that aren't there? Delighted by stories of vengeful ghosts and spirits, we largely assume there's a world outside of our regular field of vision. Whether it's inhabited is certainly debatable but the curious psychological condition called Troxler's Fading or Troxler's Effect may explain one optical illusion.
This effect is named after a Swiss physician and philosopher Ignaz Paul Vital Troxler (1780-1866), who discovered it in 1804. It is essentially a trick of perception that describes what happens if you fix your gaze upon a single point in the visual field. It doesn't even have to be for a long time – 10 seconds would do. That can make images and colors disappear from your peripheral vision.
THE LILAC CHASER
Look at the black cross at the center of the image and the spots in this "lilac chaser" illusion will fade away in a few seconds. A grey background and the cross will remain unless you are among those who will also see a moving blue-green spot. You might even notie a bunch of green spots when you move your eyes away after a while.
HOW DOES IT WORK?
Research indicates the effect is related to how neurons important for perceiving stimuli are adapted by the visual system. Unchanging stimuli will eventually disappear from our awareness while our mind will fill the areas where they used to be with the background information (or color). A "sensory fading" or "filling-in" is linked to saccades – involuntary eye movements that happen even when the gaze appears settled. If we fixate on a point, an unmoving image or scene would fade from view in a few seconds thanks to the "local neural adaptation of the rods, cones and ganglion cells in the retina," explains the Illusions Index.
The effect is made stronger if the stimulus image is low contrast or blurred.
While studies showed the effect doesn't only occur in the eyes but partially in the brain, there's not yet a definitive explanation for everything involved in this unusual visual phenomenon.
Another example image of the Troxler effect. Look at the center of the image for about 10 seconds.
And another fun example:
When it comes to time, and what the heck it actually is, there's a clash of ideas between physics and neuroscience.
If you're here to indulge in some mind-bending talk about time travel, neuroscientist Dean Buonomano is about to break some hearts. He doesn't think it's plausible—but if it were, there is one hypothesis of the universe in which it could theoretically happen. There are currently two main ideas about time: Presentism—the notion is that only the present is real: the past happened, the future will happen, but only the present exists—and Eternalism, in which the past, present, and future are all equally real. If you want to flux-capacitor your way back in time, you'll want to hope that Eternalism turns out to be the true theory. It's known to physicists as Block Universe, where all moments of the past, present, and future are already laid out in a continuum—there are places to travel to. "Under Presentism we can pretty much take the possibility of time travel off the table because there’s no other moments to go to—only the present is real," says Buonomano.
While there is certainly no consensus in the physics community, Eternalism is the standard view. And here is where the conflict with neuroscience begins. Buonomano presents the mutually exclusive ideas of the nature of time within the two fields, and explains why the disciplines need to have a meeting of the minds. Dean Buonomano is the author of Your Brain Is a Time Machine: The Neuroscience and Physics of Time.