Recently, there have been numerous examples of such images that trick the mind and leave us puzzled.

According to a study only 1% of people can see the animal hidden in the image below. This hypnotic image has been shared online but a lot of people: But can you spot the animal in the optical illusion?

Ever heard of the McCollough effect? It’s this weird trick of the mind where, after staring at a colored grating (alternating lines), your brain starts to see a pinkish tinge or other colors when looking at black-and-white lines.

Tilting your head 90 degrees may lessen or enhance it. In fact, rotating the induction images and staring at them again may actually reverse the effect. The longer you stare at the original induction images, the longer it’ll last – for hours, days, or even a few months in some cases.

This phenomenon, defined as a visual illusion in which retinal impressions persist after the removal of a stimulus, is a sort of afterimage. Researchers believe that it is a result of the continued activation of the visual system.

Namely, the strong colors make an impression on the visual system and trick it into thinking that it is still looking at the colors even when it is not, and this eventually makes one believe that what he sees are black and white stripes, tinged with red and green.

The Journal of Experimental Psychology found that in the same way as the bright flash of the camera can linger in the vision, this effect can last for over three months in case the perceiver looks at the colorful gratings for extended periods of time.

The effect is named after its discoverer, US psychologist Celeste McCollough Howard. She was the first person to ever find a so-called “contingent aftereffect”, which is an illusion that affects your brain for an extended period of time.

Over the years, there have been a number of studies done on the effect. Back in 1975, two researchers tested five groups of 16 people and, amazingly, one of the groups showed no lessening of the effect after five days. In fact, the effect remained better than half strength for four groups up to 2,040 hours later – or almost three months.

You can test the effect for yourself, with the images below. Note, there is a chance it can affect your vision for a while

Some studies have looked into just how prevalent the effect is. One way back in 1969 found that various stripes colored red and green produced the after-effects. Weirdly, it found that if your induction image was green, then you’d see red colors on vertical grates and green colors on horizontal grates. If a red induction image was used, then those colors reversed.

What’s weirder, it was only green and red that worked. “Colors near pure blue and pure yellow, which had little red or green content, produced weak aftereffects,” the study noted.. As far as we can tell, there isn’t a good explanation for why red and green are so good at producing the effect compared to others.

As for the grating thing? Well, that might be due to neurons in your visual cortex responding more strongly to their “preferred orientation and spatial frequency,” according to another study. It even suggested a rather interesting theory, that the JPEG image format used “plaid-like” (chequered) patterns, which are basically two gratings overlaid on each other.