What do you see?

Do you see gray areas in between the squares? Now where did they come from?

Disappearing Pink Circles

http://www.dougmoran.com/collections/optical-illusion-pink-dot-circle.html

Why is this happening?

Are we seeing what we are supposed to be seeing?

Recall

Images are formed on the light-sensitive layer of the

eye. What is it?

Retina

How did the Retina do it?

In the Retina…

Contains Photoreceptors

Consists of

Photoreceptors (light sensitive cells)

Rods

Cones

Rods

Contain a pigment called visual purple.

Allows them to be sensitive to dim light but only able to see black and white.

RodsFormation of visual purple requires:

The lack of Vitamin A may cause night-blindness.

Cones

3 Types of Cones:

Red

Green

Blue

Each cone contains a different pigment which absorbs light of different wavelengths.

All cones work together to allow us to see a variety of colour.

Cones do not work well in dim light (associated with bright light and colour vision.

Recall

There are 2 specialised spots on the retina.

What are they?

Fovea (Yellow

Spot)Blind Spot

Fovea (Yellow

Spot)Blind Spot

Fovea (Yellow

Spot)

Yellow depression in the retina (most central part of the retina) where images are sharply focused.

Contains the greatest concentration of cones but no rods.

Enables one to have detailed colour vision in bright light.

Blind Spot

Region where the optic nerve leaves the eye.

Does not contain any rods or cones. (no receptor)

Not sensitive to light.

How does the light get focused on the retina?

Recall

PHYSICS!!!

Ray Diagram

Focus of Image in the Eye

Characteristic of the Image on the Retina

• Upside down (inverted)

• Laterally Inverted

• Smaller in size than actual object (diminished)

But why do we see the objects as it is?

Recall

Where is the image sent after it forms on the

retina?

The Role of the Brain in Vision

The Brain interprets the image so that objects may be seen to be the right way up, front to back, and the right size.

Light Transmission Process

http://www.kscience.co.uk/animations/eye.swf

How the eye produces a focused image• Light rays from an ______enter the transparent

cornea.• The cornea ______ the light rays towards the pupil.• The light rays pass through the ______and the

________ humour.• The _____ refracts the rays to focus on the retina.• The light-sensitive cells on the ______ are stimulated

by the light of the image, and convert the _____energy into _________ energy.

• Electrical energy, in the form of nerve_________, travel along the __________ to the brain.

• The brain decodes the impulses to produce the sensation of_______ .

objectobject

refractspupilpupil

aqueousaqueouslenslens

retinaretinalightlight

electricalelectricalimpulsesimpulses

optic nerveoptic nerve

sightsight

Does this mean that our brain will process an out-of-

focus image?

What we learn today.• Photoreceptors (rods and cones)

• Functions of Rods and Cones

• The Fovea (Yellow Spot) and Blind Spot

• Image formation in the eye

• The role of the brain in image interpretation