The eye

Visual Perception

Sensation & Perception

•What is sensation?The detection or awareness of the presence

of a stimulus.

•What is perception?The process by which we make sense of the

sensations.

Object Agnosia

The visual perception system

•The network of physiological structures involved in vision, that includes:

* The eyes,* The nervous system pathways

that connect the eyes and the brain, and,

* The areas of the brain that process visual information.

Quick Quiz!

•Name as many parts of the eye as you can…

•How does light enter the eye??

The Eye

•Sense organ for vision•Major parts include:

* Cornea* Pupil* Iris* Lens* Retina

How Light Enters the eye

Anatomy of the Eye

Cornea

• The transparent coating which covers the iris and the pupil.

• Together with the help of the lens, the cornea refracts the light onto the retina.

Pupil

•The black hole in the centre of the eye (not an actual structure!).

•The size of the pupil is controlled by the iris.

•When it is very bright, the pupil is small,•When it’s dark, the pupil grows bigger to

allow more light in.

Iris

•The coloured part of the eye.•Tiny muscles inside the iris control the

amount of light that enters the eye, through the pupil.

Lens• Focuses light onto the

retina.• Ciliary muscles attached

to each side of the lens, help change the shape of the lens, according to the distance of the object being viewed.

• Once the light has been refracted onto the retina, the image which hits the retina is upside down!

Retina

• The retina contains millions of photoreceptors – known as rods and cones, that convert light into electrical impulse which are sent along the optic nerve to the brain.

Activity

•Cut out ‘The Eye’ and label each of the major components.

•Include the definition of each of the components.

•So, light reflected off objects travels in a straight line into the eye through the cornea and the pupil…

•…the light travels through the lens, which focuses it on the back of the eye, projecting an upside-down image onto the retina…

•…photoreceptors in the retina translate the image into electrical impulses which travel along the optic nerve and into the brain…

•…the brain makes sense of the signals, and tells us what we can see!

Stages of the Visual Perception System• Reception - Structures of the eye capture the

light and project it onto the retina

• It is at this stage, the photoreceptors detect and respond to light.

• The two types of photoreceptors are called: Rods and Cones.

• The stage where visual information is received.

Rods and Cones

• Rods are important for night vision

• Rods are also important for peripheral vision

• Cones are important for daylight vision, visual acuity and colour.

• Transduction - Photoreceptors (rods and cones) convert electromagnetic energy (‘light’) into electrochemical energy (‘signals’).

• You can remember transduction as the process by which light energy is translated into signals the brain can understand.

• Transmission - Neural information is sent down the optic nerve towards the primary visual cortex.

• Selection - Visual discrimination occurs which breaks down the visual stimulus into different features. This occurs in the photoreceptors and visual cortex (feature detectors)

• Organisation and Interpretation - This is the reassembling of features which is then organised and given meaning by the brain.