Visual Perception

How the eye works

How the body and mind interact.

• How does the physical reality of light from an object in the environment – referred to as a distal stimulus – cast an image on the retina – called the proximal stimulus?

• How does the image travel to the brain where it can be organised and interpreted?

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How does it happen?The actual image on our retina is:

Upside-down

Back-to-front

Blurred

Crisscrossed by a network of veins

Patched by holes

So how do we see things crystal clear?

Reception: light enters eye through the cornea and passes through the pupil. The lens then focuses the light onto the retina which contains photoreceptors- light sensitive cells called rods and cones.

Transduction: the electro-magnetic energy is converted by the rods and cones into electro-chemical nerve impulses. This allows the information to travel along the fibres to the optic nerve.

Transmission: Information is sent via the optic nerve to the primary visual cortex in the occipital lobes to continue the visual perception process.

Selection: We can’t possibly pay attention to all the millions of stimuli that enter the eye at the same time. At this point, the image is broken up by the specialised cells called feature detectors.

Organisation: When the information reaches the brain it is organised so that we can make sense of it. We do this by

Interpretation:

Sensation and Perception.

Sensation: the process where the structures of the eye receive information about the environment and transmit that information to the brain.

Perception: the process whereby the brain organises and interprets visual information.

Sensation and perception

Reception and light energyFor light energy to enter the eye it must be within the visible part of the electromagnetic spectrum. The human eye can only see between 360 and 760 nanometres from the visible light spectrum (1nm=1 billionth of a metre).

Rods and Cones Rods

There are 125 000 000 in each eye.

Responsible for vision in very low light (they are very sensitive to light).

Responsible for peripheral vision.

Concentrated at the edges of the retina.

They have low visual acuity (they can’t register detail).

They can register only in black and white.

They are most sensitive to light of approximately 500 nm wavelength.

Cones There are 6 500 000 in

each eye. They are concentrated in

the middle of the retina. They are responsible for

vision of detail. They are responsible for

colour vision (and black and white vision in daylight).

They require high levels of light to enable them to respond.

The Structure of the Eye

Ciliary muscle

What do the parts of the eye do?

Your task: Draw and label an eye and then write a

description of the function of each part.