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Copy of The Visual Perception System

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Lynette Lear

on 14 May 2014

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Transcript of Copy of The Visual Perception System

The tendency to perceive an object as remaining stable/unchanging despite any changes that may occur to the image cast on the retina.
For example, we know that a person is not getting smaller as they walk into the distance.

There are three types of Visual constancy:
1. Size

2. Shape

3. Brightness
Linear perspective


Texture gradient

Relative size –

the larger object is perceived as closer.

Height in the visual field
Visual Perception System

"mmm sandwich crumbs are the best!"
"I know there's peanuts here somewhere..."
"I'm just sayin'... if that monkey doesn't stop poking me!"
"Is that lunch grazing on the planes?"
Visual Perception System
Nervous system
areas of the
brain that
process visual
This first step of the eye receiving incoming light from the environment and focusing it onto the retina where an image of the visual stimulus is captured.
1. Reception:
The process from sensation to perception takes 5 steps
2. Transduction:
When electromagnetic energy (‘light’) hits the retina, the eye converts it to a form of energy that can be processed by the brain (electrochemical energy – which creates an electrical impulse).
3. Transmission:
Involves sending information in the form of electrical impulses along the optic nerve to the brain
4. Selection:
This stage is characterised by the filtering of incoming electrochemical energy for importance. This step of the process is unconscious to the individual, and, is important in ensuring the brain does not become over loaded with the immense quantity of information our senses pick up from our environment at any given time (This step is not in your text, but is outlined by other texts).
5. Organisation & Interpretation:
Organisation –
involves assembling or arranging the features of a visual image in a meaningful way.
nterpretation –
is the process of assigning meaning to visual information so that we can understand what we are looking at.

What happens if this stage doesn't
work properly?
Rules that we apply to visual information to assist our organisation and interpretation of the information in consistent and meaningful ways.
Visual Perception principles –
Can be classified into 3 broad categories:
Gestalt principles
Depth perception
Perceptual constancies
Ways in which we organise the features of a visual scene by grouping them to perceive a whole, complete form.

Gestalt principles include...
1. Gestalt Principles –
Ability to estimate the distance of objects and perceive the world in 3D
1. Binocular depth cues – require the use of both eyes
detects distance via changes in the tension b/w muscles in the 2 eyes as they focus on a close object.
The difference b/w the image picked up by the left eye vs. the right eye. The more different the image, the closer the object is
(basically non-existent by 10 meters)
2. Monocular depth cues – only requires one eye
automatic adjustment of the eye’s lens
Lens bulges to see items up close
Lens flattens to see objects from a distance

a created a sense of depth using drawing techniques
3. Perceptual Constancies:
2. Depth Perception:
Depth cues –

(translates 2D images from our retina into 3D vision)
sources of info from the environment
(external cues)
or within our body
(internal cues)
that help us to perceive how far away objects are and therefore to perceive depth.
The predisposition, or ‘readiness’, to perceive something in accordance with what we expect it to be.
Perceptual Set
The last 2 concepts for this chapter! 2 last things that can influence visual perception...
Emotional state
Past Experience
A misinterpretation of real sensory information
The effect of the illusion never disappears even when we are told how it works
a) Ames Room b) Muller Lyer
Draw and label the eye using the following diagram as a guide.
The retina is the back part of the eye that contains the cells that respond to light. These specialized cells are called photoreceptors. There are 2 types of photoreceptors in the retina: rods and cones.
The rods are most sensitive to light and dark changes, shape and movement and contain only one type of light-sensitive pigment. Rods are not good for color vision. In a dim room, however, we use mainly our rods, but we are "color blind." Rods are more numerous than cones in the periphery of the retina. Next time you want to see a dim star at night, try to look at it with your peripheral vision and use your ROD VISION to see the dim star. There are about 120 million rods in the human retina.

The cones are not as sensitive to light as the rods. However, cones are most sensitive to one of three different colors (green, red or blue). Signals from the cones are sent to the brain which then translates these messages into the perception of color. Cones, however, work only in bright light. That's why you cannot see color very well in dark places. So, the cones are used for color vision and are better suited for detecting fine details. There are about 6 million cones in the human retina. people Some people cannot tell some colors from others - these people are "color blind." Someone who is color blind does not have a particular type of cone in the retina or one type of cone may be weak. In the general population, about 8% of all males are color blind and about 0.5% of all females are color blind.
Cow's eye dissection video http://www.exploratorium.edu/learning_studio/cow_eye/video_big_all.html
Class activity - using the laminated copies of 'The forest has eyes', how many faces can you see? Circle them.
What do you see in this picture?
Comparison between rods and cones:
125 million each retina
function best in low levels of light
black, white and shades of grey vision
low level clarity
responsible for peripheral vision
higher concentration in the outer regions of the retina
respond best to shorter wavelengths
6.5 million each retina
function best in high levels of light
provides colour vision
high level of clarity
responsible for central vision
concentrated in the centre of the retina
responds best to longer wavelengths
Summary of Visual Perception System
Reception, transduction and transmission = Sensation

Selection, organisation and interpretation = Perception
Visual sensation
purely physiological
same for all those with 'normal' vision
one person will always receive the same sensation from the same sensory input
acts independently of other senses
Visual Perception
physiological and psychological
potentially different for two people observing the same thing
one person can perceive the same sensory input in different ways
can be influenced by input from other senses
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