Our eyes give infomation about an object, this infomation can include:
Perception- The way the brain make sense of the visual image detected by the eyes.
Retina- The light-sensitive layer at the back of th eye, made up of nerve cells called rods and cones.
Rods- Light-senstive cells in the retina that respond even in dim light.
Cones- Light-sensitive cells in the retina that detect colour.
Optic Nerve- Bundle of nerve cells that leads out from the retina at the back of they eye, it carries info from the rods and cones to the brain.
Seeing, or vision is the process of detecting light from objects. It is a biological process, that happens in our eyes. Perception is more than that. Perception is the way we make sense of the visual image. This happens in the brain and allows us to understand what we see.
Perception = Psychological Process of making sense of the visual image.
Vision = Biolgical Procces of seeing.
Structure Of The Eye
The light reflected from an objact enters the eye and makes an image on the retina a layer at the back of the eye. The is sensitive to light and send nerve impulses to the brain. This is possible because the retina is covered with thousands of cells which can detect light, there are two types of retina cells:
The Structure Of The Retina
The rods are very senstive to light and they also respond to movement. A rod cell will respond even when only very dim light falls on it. They are found mainly around the edge of the retina.
Cones are mainly found in the centre if the retina, in a soecial area just opposite the 'hole' (pupil) at the front of each eye. This helps us to see clearlyand in detail as there are lots of cones packed very close together. They are also less sensitive to light than rods, so they only work in bright light, unlike rods though, cones detect diffrent colours of light.
Nerve Impulses From The Retina To The Brain
Rods and cones are special nerve cells. When enough light falls on a rod or a cone, the cell responds by sending a nerve impulse. All the nerve impulses froms rods and cones across the whole retina are sent to brain. The nerve impulses travel along other nerve cells which are bundled together in the optic nerve. This looks like a thick stalk at the back of the eye. The Nerve impulses in the optic nerve are carried to the brain.
The Optic Nerve And The Brain
For psychologists, the ‘blind spot’, is part of the world we cannot see.
What Causes The Blind Spot?
Earlier it was described how the retina responds when light from an object falls onto the rods or cones and that the optic nerve carries messages to the brain. At the point on the retina where the optic nerve leaves the eye, there is no space for any rods or cones. This little area is therefore ‘blind’. If the light from an object falls onto that part of the retina there are no light-sensitive cells to detect it. This area of the retina is called the blind spot. There is a blind spot in each eye. Part of your vision isn’t missing, because the two blind spots don’t overlap, so even if one eye can’t see something, the other one can.
Blind Spot- The area of the retina where the optic nerve leaves. It has no rods or cones so cannot detect light.
Optic Chiasma- The cross-shape where some of the information from the left and right eye crosses over to pass into the opposite side of the brain.
Visual Cortex- The area at the back of the brain that interprets visual information.
You can find the blind spot in the one eye by closing the other. Try with the picture below.
The Optic Chiasma
The information from the retina goes along the optic nerve to the brain. Information from each eye goes to both sides of the brain. Some from the left eye goes to the left side of the brain, and some the right. Similarly, some information from the right eye goes the left side of the brain, and some to the right. Information from the left and right side crosses over at a point called the optic chiasma.
From the optic chiasma, visual information is carried to the back of the brain. Many perceptual processes happen in an area called the visual cortex. The job of the visual cortex is to interpret the information from the rods and cones.
The visual cortex uses this information in perception to understand shapes and distance. It also fills in the gap left by the blind spot in each eye. This is why a pattern seen with one eye looks complete even when part of it falls on the blind spot.