Visual Percepti

onChapter 3

Pages 75-125

Every day we are bombarded by information from the environment (stimuli)

Our body receives this information via our senses.

We have five senses: what are they?Out of all the information that comes to us we

only attend to a small amount of it due to selective attention.

By doing this we can filter out information that isn’t important and only pay attention to what is important to us.

We see the world with our eyes but our brain interprets what we see.

Each sense that captures information (ear, eyes, nose) has specialised cells that transmit the information to the brain to be interpreted. This is known as a sensation.

Perception

• Perception is the mental process of receiving, organising and interpreting information received by our sense organs into meaningful objects.

Characteristics of the Visual Perception

System

How do we see?How do we interpret visual sensations?

Characteristics of the Visual Perception System

• The eye can only see electromagnetic energy:This is the physical and external energy that

comes from the environment.

Physical energy Sense organ

Electromagnetic energy Vision

Mechanical energy Hearing and touch

Chemical energy For taste and smell

Electromagnetic Energy

• Consists of particles of energy that travel in waves of different sizes. The entire range is known as the Electromagnetic Spectrum.

• It is divided into sections according to frequency and wavelength.

• The human eye can only detect a small portion of the electromagnetic spectrum which is called “visibly light”.

• The visible light spectrum ranges in wavelengths from 380nanometres-760nanometres

Characteristics of the Visual Perception System

1. The eye detects electromagnetic energy.2. Receptor Cells convert the energy into a

neural impulse (electrochemical message that travels along neural structures to reach and communicate with the brain)

3. It changes form otherwise the brain wont be able to understand it.

Detecting and Focusing Light

In a nutshell, in order for vision to occur 2 things need to happen:

1. Light needs to travel through the eye and produce a focused image on the retina.

2. The retina needs to convert this image into a neural impulse which can be sent to the brain to be interpreted.

1. Light enters eye through Cornea.

2. Light passes through the Aqueous Humour.

3. It then goes through the pupil which is surrounded by the Iris. The muscles in the Iris contract and expand depending on the amount of light it wants to enter.

4. Light then passes through the Lens which focuses the image onto the retina.

5. Then the Vitreous Humour.

6. The image is then captured by the Retina.

7. When the image is on the retina it is upside down and back to front.

8. Message then gets sent down the optic nerve to the brain where it is interpreted.

http://www.youtube.com/watch?v=LpjbOhtcD0A&feature=related30sechttp://www.youtube.com/watch?v=gvozcv8pS3c&feature=related2min39

Converting Light into a Neural Impulse.

• In order for the brain to understand, the electromagnetic energy (light) needs to be converted into a neural impulse by the receptors cells.

• This is done at the RETINA.• The retina consists of a number of layers beginning

with specialised receptor cells that convert this energy. These receptor calls are called PHOTORECEPTORS.

• Photoreceptors convert the electromagnetic energy into electrochemical energy.

Photoreceptors

• There are two types of photoreceptors.1. Rods2. ConesThey both detect and absorb light. Once light is

absorbed the rods and cones generate a nerve impulse which stimulates neighbouring cells called Bipolar which then transmit the information to Ganglion cells. Ganglion cells pass the information along the optic nerve to the brain for interpretation.

Rods Cones

•125mill rods in each retina•More sensitive to light•Help us see in dim light•Assist our vision at night•Found in the outer regions of the retina•Responsible for peripheral vision•Detect less detail •Takes 30min to adapt to dark conditions

•6.5mill cones in each retina•Enable us to see colour•Work best during the day•Operate poorly in dim light•Found in the centre of the retina•Also found in the fovea (located in the centre of the retina and only contains cones (50,000)•Cones enable visual acuity (detection of fine detail)

ThresholdsLimits of our sensory abilities.

Absolute threshold: the lowest level of a stimulus that a person can detect. Needs to be seen 50% of the time

Vision: candle flame seen at 50km under ideal conditions 50% of the time.

Differential threshold: the smallest difference or change that can be discriminated between two stimuli.

Visual Perception Process.Page 88-90

Reception Transduction Transmission Selection Organisation Interpretation

Refer to text book and handout.

• Lets have a read of page 89