There is an old saying in China— Seeing is believing.Can you believe everything you see？Sometimes our eyes see something，and our minds understand it easily.At other times，we may look at something called an optical illusion.The word optical means "related to sight"----the way we see things with our eyes.An illusion is something that seems to be real but in fact it is not.
    Look at these optical illusions.Sharing what you see and what your classmates see，you will find the way we see things is often personal，so you may not see things the same way as someone else.

	Which black dot is larger？     Most people say it's the dot on the left.Now measure（測量） the black dots.The black dot on the left may seem larger because of the small white dots around it，but they're really the same size.
	Look at this picture.What do you see？     Do you see a cup，or do you see two faces？Now look again!The illusion shows two different images（圖像） at the same time.So our brains have to choose which image to look at.One part of the brain"sees"the cup and another part "sees"the faces，so the image keeps changing.
	Are the circles moving？     When you look at this picture for a long time，your mind may tell you that the circles are moving，but this is impossible!How can a picture move？Some people think the circles seem to move because，often，when we see circle-in-circle shapes，like in car wheels or snake bodies，they are usually moving in life.Our brains often see these shapes move.So when our eyes see this shape，our mind thinks that the image is moving.Other scientists believe the illusion of movement is caused by the very small movements of our eyes.

（1）

in disagreement

in disagreement

（2）

different from

different from

（3）

working

working

（4）

get used to

get used to

（5）

Examples

Examples