Unit 1: Perception & Dreaming How do we see our world?

THE EYE!

Starter Activity Keeping your eyes SHUT, take an item out of the bag. Without looking at it, what can you tell? What shape is it? How big or small is it? Feel it’s texture – is it hard/soft/furry/slimy ? What else can we tell about it without using our eyes? What can’t we tell about it? What colour is it?

Make a list! Don’t need your eyesNeed your eyes

Vision vs Perception What is the difference between them? Vision: Our eyes work by DETECTING rays of light that are reflected or emitted by objects. This is a biological process that happens in our eyes. Perception: happens in our brain. It is a psychological process during which our brain makes sense of the visual image detected by our eyes.

The Structure of the Eye Draw and label a diagram of the eye

How do we see? FAp_w

How do we see? 1.Light is reflected off an object, enters the eye, and makes an image on the retina (the layer at the back of the eye). 2.The retina is covered with thousands of light- detecting cells called rods and cones. 3.The retina, which is very sensitive to light, sends nerve impulses to the brain. The nerve impulses travel along the optic nerve.

Chain of events retina Light is reflected off the object and enters the eye

The Retina Rods and cones are special nerve cells. Using your textbook, make a table listing the differences between them. RodsCones

Table listing the differences between rods and cones RodsCones Respond in dim lightWork best in bright light Detect light, shape and movement but not colour Detect colour, but less sensitive to light than rods ADDITIONAL INFO Located on edge of retinaLocated in centre of retina 120 million in each retina6 million in each retina Responsible for detecting objects ‘out of the corner of your eye’ If there is not enough light, cones cannot detect the colour of an object. Task ~ can you create a poem to help remember the main points!

What happens when you go to a movie ? Sequence of EventsRodsCones 1.You are outside in the bright sunshine, just about to go in to the movie theatre 2.You step into the theatre. You can’t see a thing! Your eyes haven’t adjusted to the dark. You can vaguely make out 3.After a few minutes, you can make out people and shapes, but no colours. 4.Movie finishes, and you step outside. It is too bright! It is difficult to see! 5.Finally, after a few minutes, your eyes adjust, and everything looks normal again.

What happens when you go to a movie ? Sequence of EventsRodsCones 1.You are outside in the bright sunshine, just about to go in to the movie theatre -active 2.You step into the theatre. You can’t see a thing! Your eyes haven’t adjusted to the dark. You can vaguely make out -active 3.After a few minutes, you can make out people and shapes, but no colours. active - 4.Movie finishes, and you step outside. It is too bright! It is difficult to see! active - 5.Finally, after a few minutes, your eyes adjust, and everything looks normal again. -active

How do nerve impulses get from the retina to the brain? When enough light falls on a rod or cone in the retina, the cell responds by sending a nerve impulse to the brain. These impulses travel along the OPTIC NERVE. The optic nerve looks like a thick stalk at the back of the eye, and consists of nerve cells bundled together. Once information reaches the brain, whatever the eye h as seen can be interpreted.

Chain of events retina Light is reflected off the object and enters the eye brain Nerve impulses travel along the optic nerve to the visual cortex

The optic nerve and the brain At the point in the retina where the optic nerve leaves the eye, there is no room for rods or cones. This area is called the ‘blind spot’, and it occurs in both eyes. Light landing on the blind spot is not detected by the eye. We don’t notice our blind spots, because they don’t overlap. If one eye can’t see something, the other one can. When you have both eyes open, you are never aware that part of each visual field is ‘missing’.

The blind spot To find your blind spot draw the image below on a scrap of paper Close your left eye. Hold the image (or place your head from the computer monitor) about 20 inches away. With your right eye, look at the dot. Slowly bring the image (or move your head) closer while looking at the dot. At a certain distance, the + will disappear from sight...this is when the + falls on the blind spot of your retina. Reverse the process. Close your right eye and look at the + with your left eye. Move the image slowly closer to you and the dot should disappear.

The optic chiasma Information from each eye travels along the optic nerve to each side of the brain. Information from the left and right eye crosses over at a point called the optic chiasma.

The brain Visual information travels to the back of the brain, where it is interpreted, and where the perceptual processes occur. The part of the brain responsible for this activity is the visual cortex. There is a visual cortex in each hemisphere of the brain. It is only once the information reaches the brain that shapes, distances and colours are understood. The visual cortex also fills in the gap left by the blind spot in each eye. Task ~ Draw and label the brain!

Chain of events retina Light is reflected off the object and enters the eye brain Nerve impulses travel along the optic nerve to the visual cortex Visual information is interpreted. The object is recognised.

Questions 1.Where are the light sensitive cells in the eye? 2.What travels along the optic nerve? 3.What cells do we use to detect I.a bird flying at night? II.the colour of the bird in bright daylight? 4.What is missing from the blind spot to make it blind? 5.I s colour detected on the retina or in the brain