Area of Study #2 Visual Perception

Perception

Imagine you are sitting on the sofa, reading a book. While reading you become aware of a slight, unidentifiable sound behind you.

It could be the sound of a leaf moving against the window, a footstep in the street outside or someone moving in another part of the house.

You turn in the direction of the sound and discover that the cat has jumped on a chair and is now licking its paws.

The image has made some important points about human perception.

Firstly, you become aware of something that is unidentifiable happening nearby.

Initially you simply sense the sound and nothing more.

Then, as you turn and look in the direction of where you heard the sound, you perceive the cat and the meaning of the earlier sound becomes clearer.

The jumping of the cat initiated sound waves, a form of mechanicalenergy caused by the vibration of air molecules, to travel to your ears.

The pattern of sound impinging on your eardrums served as the stimulus that resulted in your state of awareness. This in turn led to you paying closer attention to the momentary sensation and your actions of turning and perceiving the cat.

What is vision?

• The act or power of sensing with the eyes; sight.

• The ability to see; the visual faculty

• The perceptual experience of seeing; "he had a visual sensation of intense light"

What do you see?

Is this easier to perceive as a cow?

What features make the perceiving of a cow in this figure easier than in the previous picture?

Visual SensationVisual Sensation

• What is visual sensation?

• The initial process of detecting and decoding environmental information

• When you look at the first picture of the cow, your eyes transmit information to your brain about which parts are white and which parts are black.

Visual Perception

• What is visual perception?• organising, interpreting and giving

meaning to what the eyes initially process.

• Perception occurs when the information transmitted to your brain is meaningfully interpreted. (When you organised the black and white patches into the shape of a cow)

Visual Sensation vs. Perception

Sensation

- Physiological process: involves neurological reactions to physical energy sources

- Process is the same for everyone

- Involves: Reception, transduction, transmission

Perception

- Psychological process: involves giving meaning to the sensory information.

- Outcome may differ between individuals

- Involves: Selection, organisation and interpretation

The Process of Sensation and Perception

The Visual Perception System

• The visual perception system consists of the complete network of physical structures involved in vision.

• The system includes: - All the parts of the eyes - The neural pathways that connect the

eyes and the brain - The visual processing areas of the brain

The structure of the eyeCornea – The front covering of the eye that covers the iris and pupil

Pupil – the opening in the centre of the iris. The size of the pupil determines the amount of light that enters the eye.

Iris – The coloured part of the eye. The muscles of the iris change the size of the pupil

Lens - transparent flexible structure in the eye that focuses light on the retina by changing shape

Retina – a multi-layered sensory tissue that lines the back of the eye.  It contains millions of photoreceptors that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images. 

Optic nerve - The optic nerve transmits electrical impulses from the retina to the brain

Blind spot – Because the optic nerve does not contain receptor cells (like on the retina, there is a blind spot.