Visual SensationVisual Processing

Artificial Senses - Sight

Human Eyeball

A. Sclera

• Basically, this is the white of the eye. Attached are six exterior muscles, which enable us to look left, right, up and down.

B. Vitreous

• This fluid preserves the spherical shape of our eyeball, as well as helping to support the retina.

C. Cornea

• Transparent protective coating over the front part of the eye

D. Iris • The colored part of the eye – this

muscle dilates or contracts the pupil to allow more or less light to enter

E. Pupil

• The small, adjustable center of the iris that allows light to enter the eye

F. Lens • Flexible enough to focus on objects near

or far (accommodation) – if an object is very close is gets smaller and rounder; if an object is further away, it get larger and wider

G. Retina • Inner lining of the back of the eyeball –

the lens focuses an image from the outside world on the retina

Rods and Cones

• Rods determine shades of light and dark. Cones determine color.

H. Fovea

• On the retina, directly behind the lens. The area of sharpest picture.

I. Optic Nerve

• Takes the visual information from the eye and sends it to the brain for processing. Different parts of the brain interpret what the shapes, colors, motion, depth, etc. we see are, and tell us what it is, and what to do with it.

Fovea

• On the retina, directly behind the lens. The area of sharpest picture.

• Acuity – the sharpness of vision• Nearsightedness – the misshapen

eyeball focuses light rays in front of the retina – you will see near objects well, but not far away objects

• Farsightedness – the light rays from nearby objects reach the retina before they have been focused – you will see far objects better than near objects

Color Vision

• There are two theories of color vision:–Trichromatic Theory–Opponent-Process Theory

Young-Helmholtz TheoryTrichromatic Theory

• Rods and cones are pre-set to be sensitive to RED, GREEN, and BLUE. All of the colors that we see are combinations of those three colors.

Opponent-Process Theory

• Sensory receptors in the retina come in pairs:–Red/Green–Yellow/Blue–Black/White

Opponent-Process Theory• If one sensor is stimulated, the other is inhibited• If one sensor is over-stimulated, and fatigues,

the paired sensor will be activated, causing an afterimage

• If a person is missing a particular pair of sensors, they will be colorblind to those hues– Dichromatic Color Blindness have difficulty seeing

shades of red and green, or yellow and blue

Color

• Hue – the different colors that we see and the name given to a color

• Saturation – the richness or vividness of a color

• Brightness – how close a color is to white or black

• Hue – determined by the wavelength (the distance from one wave peak to the next) of the light wave that the eye is receiving

• Brightness is influenced by the height of the waves (amplitude) of light that are received by the eye

• The shorter the wavelength, more bluish colors

• The longer the wavelength, more reddish colors

• The higher the wave, more yellowish• The lower the wave, more greenish