
Optical illusion tests, as the name suggests, are fun and engaging tests that claim to boost your brain functioning. How? These are strange images with one or more elements in them; the idea is to spot them in a specified time limit to test how sharp your brain and observation skills are.

For example, this particular test is based on an image which has a grid filled with the number 19. However, there are two different numbers-- 16 and 91-- hidden between the 19s in this picture. The challenge is to spot the numbers 16 and 91 in the above image in just 7 seconds. If you do, then you are one of the few smartest people to do so.

Ready to take this challenge? Simply close your eyes and relax. Now, look at the image in the above slides with a fresh mind and quickly try to figure out the odd numbers 16 and 91 among the 19s. Notice how long it took you to spot the numbers.
If you figured them out within 7 seconds, then you are smart. But, if you didn't then worry not.

Steps to spot the numbers 16 and 91 in the optical illusion above:
1. Look at the above image with a calm mind.
2. Look at each number closely in a strategic manner, instead of randomly looking at the image.
3. Go column-wise and look closely at the numbers.
4. You'll soon be able to spot number 16 in the second column, second row. Whereas, number 91 is at column 14, second-last row.

This test puts your visual discrimination skills to the test, which is the ability to notice tiny differences between similar-looking numbers and patterns. This can help you make faster and accurate visual decisions in your daily life.