You're about to experience a phenomenon known as motion-induced blindness, a quirk of the human visual system that makes us fall for some seriously strange optical illusions.
Experiencing the illusion is simple. Click on the GIF below to enlarge, then focus on the flashing red dot at the center of the rotating orange square. Take care not to move your eyes whatsoever. Almost immediately, the three yellow dots seem to fade into nothingness, disappearing from sight. Shift your gaze even slightly, however, and they instantly reappear.
GIF via NatGeo's BRAINGAMES blog
This illusion highlights a quirk of perception that can be interpreted as a feature, a bug, or both. On one hand, it seems like a defect to have something directly in your field of view disappear from sight. Then again, perhaps it makes sense for our brains to ignore a stationary object amidst a slew of dynamic ones. (Imagine, for example, how such an ability might be useful while stalking prey.) Was this visual trait advantageous at some point in our evolutionary history? It makes you wonder to what extent this peculiarity of perception is conserved throughout the animal kingdom, though its ubiquity would be pretty damned difficult to test for empirically. Try training a dog to fixate on a spot, let alone asking it whether dots are disappearing from its field of view.
Whether humans experience the effects of motion-induced blindness in a real-world setting – while driving, for instance – remains poorly understood, though researchers have given it some thought. Via Nature News:
Researchers speculate that this phenomenon could happen in everyday life without us noticing it. A highway at night, with drivers staring dully at a mass of moving lights, might recreate the kind of conditions used in the experiments, says [Yoram Bonneh, whose team formally named the phenomena in 2001], causing objects – the tail lamp of the car in the next lane, for example – to temporarily vanish.
Motion-induced blindness is just one in a slew of known "visual disappearance" phenomena, one of the most well-known examples of which is exemplified by the Troxler effect, discovered by Ignaz Paul Vital Troxler in 1804. Focus at the center of this animation, and watch as the dots around the perimeter disappear:
It's worth pointing out that these effects are not a direct consequence of the physiological blind spot in human vision (though that can give rise to some cool optical illusions, too). In fact, researchers in 2004 drew a connection between motion-induced blindness and perceptual filling-in (PFI), a similar visual phenomenon that is thought to help our brains reconstruct the information lost on account of our blind spot.