How do my eyes play tricks on me?
If you feel like your eyes are playing tricks on you, it could be real because our eyes will play tricks on us. Some people call them optical illusions. Now, if you want to look at this, I have two identical pieces of plastic and one is yellow, and this one is red. Now I'm quite strong so I can actually pull this yellow one from behind and make it longer and bigger. Watch, I'll pull. [Professor Gizmo pulls the yellow piece and extends it past the edge of the red piece] There. Now, I will show you. Look at how much bigger it is. I did that. Now tell you what, we can put it back the same size. Oh what, you want to see me do the red one? Well, sure! Here, turn it around and I'll pull the red one, I'll make it bigger. [Professor Gizmo pulls the red piece of plastic and extends it past the edge of the yellow piece.] There, it looks bigger. Let's put is side by side. Yes! It is bigger. Now, you know what, our eyes are just playing a trick on us. It's really not bigger. Watch, I put them back together and they are exactly the same size. OK. Now, if I put the red one down below, guess what, the red one is bigger. If I put the yellow one down below, the yellow one's bigger. Our eyes are playing tricks on us because we look at this object as our eyes see it, and they're just turning it around. You could probably do this with bananas too, because they are the same shape and If I turn it this way, [Professor Gizmo hold the pieces of plastic up, the yellow piece on the right and the red piece on the left] one looks bigger. If I swing around like this... [Professor Gizmo swaps the pieces around so that the red piece is now on the right] So, you can't always trust your eyes because sometimes they're playing tricks on us. The reason this is happening is because of perception, OK When we have it like this [he puts the pieces one on top of the other] you can see, if I turn this around, that they are both identical; they are both exactly the same size. When I go down like this - one over the other - this end appears to be short over here and short over here but when I move it up it's exactly the same length. This is because of where it falls on this elliptical shaped object here; it makes our eyes go "Oh, well look, there is a space there and a space there; this one must be bigger." So, our eyes are just tricking us into thinking that this one is bigger. When I switch it around, look again, identical size. I put this one below it, and we now have that same illusion. That's why our eyes play tricks on us.
