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Vision

You can’t always trust your eyes

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How many legs does this elephant have?

Color –Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world.

The Anatomy of Visual Sensation

• Visual cortex –Part of the brain – the occipital lobe –where visual sensations are processed.

From Sensory Organs to the Brain

The process of sensation can be seen as three steps:

Reception--the stimulation

of sensory receptor cells

by energy (sound, light,

heat, etc)

Transduction--transforming

this cell stimulation into neural impulses

Transmission--delivering this neural

information to the brain to be

processed

Transduction• Receptors –

Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse.

• Sensory pathway –Bundles of neurons that carry information from the sense organs to the brain.

Phototransduction:Conversion of light energy into neural impulses that the brain can understand.

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Wavelength (Hue)• Hue (color)

the color experienced.

• Wavelength isthe distance from the peak of one wave to the peak of the next.

• Intensity(perceived brightness,)is determined by the amplitude of the wavelength.

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Wavelength (Hue)

Different wavelengths of light resultin different colors.

Long wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

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Intensity (Brightness)

Blue color with varying levels of intensity.As intensity increases or decreases, blue color

looks more “washed out” or “darkened.”

10http://www.youramazingbrain.org.uk/supers

enses/brightness.htm#

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VisibleSpectrum

The Stimulus Input: Light EnergyB

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The Eye

Jupiterimages/ Thinkstock

The Eye

1. Cornea: Transparent tissue where light enters the eye. (COVERS get it Cornea)

2. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.

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The Lens

Lens: Transparent structure behind the

pupil that changes shape to focus images on the

retina.

Accommodation: The process by which the

eye’s lens changes shape to help focus near or far

objects on the retina.

• Retina –Light-sensitive layer at the back of the eyeball

• Blind spot: no receptors where information exits the eye

– The visual system uses information from cells around the blind spot for “completion,” filling in the blind spot

• Fovea: high acuity area at center of retina

The Retina

Optic nerve –Bundle of neurons that carries visual information from the retina to the brain.

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Test your Blind Spot

Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At

some point the car on the right will disappear due to a blind spot.

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A B

CD

1. Which, of the 4 choices above, is the human eye most likely to see as a bright blue color?

2. The lens of the eye changes shape to aide in focusing on near or far objects. This phenomenon is known as _______________________.

3. The muscle that expands and contracts the pupil, and also gives eyes their “color,” is

the ______________

4. The phenomenon that addresses how you can pick out your friend’s voice and

process what she is saying while surrounded by large numbers of other people carrying

on their own conversations is known as the _______________________________.

How We See: Are You Nearsighted or Farsighted?

▪ In people with normal

vision, both nearby and

faraway objects are

focused on the retina at

the back of the eye

▪ In nearsighted people,

faraway objects are

focused in front of the

retina

▪ In farsighted people,

nearby objects are

focused beyond the

retina

How we see – near and farsightedness

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Accommodation:The lens changes shape to focus near or far objects on the retina.

Rods

tinted

yellow

Cones

tinted

purple

▪ Located in periphery of

retina, peripheral vision

▪ Function in dim light

▪ Detect black, white, and

grey, but not colors

▪ Does not detect detail

Rods

▪ Near center of retina

(fovea)

▪ Function in bright or day

light

▪ Detect fine detail

▪ Enable color perception

Cones

Photoreceptors