Topics: Dream, Sleep, Depth perception Pages: 20 (4720 words) Published: April 27, 2013

Vision | The biological process of seeing |
Perception | The psychological process of making sense of an image | What is perception?
* This is how we see and understand the world
* The two key things about perception are:
1. How we see distance or depth
2. What goes wrong when we are fooled by an illusion

The structure of the eye

1. Light enters through the cornea. The cornea focuses the light and passes it through the pupil. 2. The lens re-focuses the light that has come through the pupil, projecting the focused image on the retina. 3. Cells in the retina convert the light forming the image to electrical impulses, and the optic nerve takes the signal to the primary visual cortex of the brain. 4. The signals tell our brains about the colour, size and distance of the objects

The Retina
* The retina is very important for perceiving images
* It is covered in nerve endings
* It transmits signals to our brain so we are able to interpret what we see * There are 2 types of cells in the retina- Rods & Cones Rods| Cones|
* Are very sensitive to light * They allow us to see in dim lighting conditions * Do you ever think you have seen something in the corner of your eye? * This is just a very subtle hint of light that passes us * Because the retina is so sensitive we see this | * Allow us to see clearly and in detail * They only work in good lighting conditions * They detect colours * This is why we can’t see colours in darkness. The cones can’t work properly|

The Blind Spot
This is the area of the retina where the optic nerve leaves. It has no rods or cones so cannot detect light. There is a blind spot in each eye. Our brain ‘fills’ in the gap so we are never left blind. It does this by filling in with the background surrounding what you can see.

This is the ‘x’ shape in our brain where information
from each eye crosses over to the opposite side of the brain.

This is the ‘x’ shape in our brain where information
from each eye crosses over to the opposite side of the brain.

The Optic Chiasma The Visual Cortex
The visual cortex understands depth, distance, shape and size

Visual Cortex
Visual Cortex
Optic Chiasma
Optic Chiasma

Visual Constancies
* Our brain also uses a very clever tool called constancies which allow us to know the size of objects and to understand that they do not suddenly change shape or size but are just moving Size Constancy

* Our brain makes a mental adjustment so that we know how ‘big’ things actually are * Eg, we know that if someone walks towards us they are just getting closer, they are not growing into a giant before our eyes! Shape Constancy

* This is objects are perceived as having the same shape even when viewed from different angles * Eg, you can swirl a pen in front of your face. The pen is changing direction but it’s shape remains and our brain knows it is still a pen! Colour Constancy

* The perceived colour of objects remain the same even when the lighting conditions change * Our brain compares the object to our environment to make a judgment about the colour it is * Eg, we know Oranges are still orange even if the room gets darker!

Binocular Depth Cues
* Bi means two so binocular depth cues refer to when you judge depth using both eyes. * They are natural abilities.
* Steropsis

* The brain compares images from the left and right eye to form a 3D image (very similar to binocular disparity) * If the 2 images from the different eyes are very similar then the object is far away * If the 2 images have differences the object is closer

Monocular Depth Cues
* Mono means one. Therefore we are able to judge things using just one eye * Therefore we rely on hints in the environment to help us. Texture gradient
* Texture or gradient becomes finer as it gets further away...
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