Can you trust your own eyes?

Don’t be so sure. Check out these optical illusions and see if you fall

for their trick.

1. Do all of these horizontal lines actually bend?

The lines are all straight – and parallel. They appear to curve because of a trick played on neurons in the visual centre of your brain. The retina sends signals to the part of your brain where edges and lines are created. But the shapes and shadings of this “café wall” illusion play havoc with the signals by both exciting and depressing the brain cells. In trying to interpret the muddled message, the brain decides the lines are bent.

2. Which step in this staircase is lowest?

Look for that lowest step and you just go round and round, getting nowhere. When your eyes and brain take in those straight, two-dimensional lines that form the staircase, they turn them into three dimensions. But they can only do this for one part of the picture at a time-say, a corner where the stairs turn and descend – not for the whole image at a glance. So you keep seeing pieces that make sense, even though the staircase itself is impossible.

3. Do the lines here form a spiral

The spiral you see doesn’t exist. Instead it’s a series of complete circles. Try tracing one with a pencil and you’ll see. The slanted black and white segments that make each line look like twisted cords. Those segments cause the visual neurons in your brain to signal that the circles slant inwards, creating a false spiral.

4. Are there dots at the intersection of the white lines?

No. Your visual neurons are being duped once more, this time by the play of light and dark. The precise spacing here between the blue corners of the squares and the white intersections gives the neurons the double whammy. Some cells are stimulated while others mellow out. The result: grey dots that seem to appear and then vanish if you look right at them.

5. Which one of the red ball is smaller?

The red balls are exactly the same size. But the one on the left looks smaller because we tend to make visual judgments – color, brightness, distance, size – by comparing nearby objects. In this case, the mind is fooled because one red ball is small compared to those surrounding it, while the other is large next to those around it.