VisionEYE see

you!

Transduction Transduction: Technically speaking,

transduction is the process of converting one form of energy into another.

As it relates to psychology, transduction refers to changing physical energy into electrical signals (neural impulses) that can make their way to the brain.

Vision: Transduction and Light Energy

Transduction: Our eyes have the ability to convert one form of energy – in this case LIGHT – into messages that our brain can interpret as a visual experience

We can only see a small part of the electromagnetic spectrum

The Physical Properties of Waves

These properties apply to audition (hearing), too: • The higher the frequency, the higher the pitch and vice versa• The greater the amplitude the louder the sound and vice versa

The Structure of the

The Structure of the Eye

The Structure of the Eye

Cornea = outer covering of the eye.

The Structure of the Eye

Pupil = the adjustable opening in the center of the eye through which light enters.

The Structure of the Eye

Iris = a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.

• The iris dilates/constricts in response to changing light intensity

The Structure of the Eye

Lens = the transparent structure behind the pupil that changes shape to help focus images on the retina.

The Structure of the Eye

Retina = the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing

of visual information.

The Visual System Cornea

Transparent protective coating over the front of the eye

Pupil Small opening in the iris through

which light enters the eye Iris

Colored part of the eye Lens

Focuses light onto the retina Changes shape through

accommodation to help focus image on retina

Retina Lining of the eye containing

receptor cells that are sensitive to light

Fovea Center of the visual field

Properties of Color and Light Energy

Hue Colors we see such as

red and green Determined by

wavelength Shorter wavelength

results in blue-violet; longer results in red

Brightness “loudness” or intensity of

a color Determined by

amplitude Saturation

Vividness of a hue

The EyeThe Retina

Rods and Cones

RodsCones

Receptor Cells Cells in the retina that are

sensitive to light Visual receptors are called rods

and cones Rods

About 120 million rods Respond to light and dark Very sensitive to light Provide our night vision

Cones About 8 million cones Respond to color as well as light and

dark Work best in bright light Found mainly in the fovea

Marker Demonstration? Stars in the sky?

Rods & Cones One to try at home: In a dark room (or

outside) focus on an image or object. Notice how detailed the object appears. Then focus your foveal vision just to the side of the image or object you were looking at. You should notice that the image becomes more detailed

The EyeThe Retina

Optic nerveBlind spotFovea

The Structure of the Eye

Blind Spot = the point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there.

The Structure of the Eye

Fovea = the central focal point in the retina, around which the eye’s cones cluster.

The Structure of the Eye

Optic Nerve = the nerve that carries neural impulses from the eye to the brain.

Pathways from the eyes to the visual cortex

From Eye to Brain Optic nerve

Made up of axons of ganglion cells

carries neural messages from each eye to brain

Optic chiasm Point where part of

each optic nerve crosses to the other side of the brain

Thalamus relays sensory info to visual cortex in occipital lobes

Visual information processing

Visual information processing

Feature Detection Feature detectors are neurons in the brain that

respond to specific aspects of a stimulus: edges, lines, movements, angles Feature detectors in the visual cortex send signals to

other areas of the cortex for higher-level processing These areas – called supercell clusters – work in teams to

determine familiar patterns – such as faces (processed in the right-side of temporal lobe)

Parallel processing Our brains process multiple features of visual experience

at once and integrate these features to create our experience of vision

If parts of this integration are disrupted through damage or electromagnetic pulses, we may lose our ability to processes certain aspects of vision such as movement or lines (blindsight)

Stuff you should know How the eye works with the thalamus

and the occipital lobes (review) Feature detector cells The significant difference in number and

function of rods and cones How parallel processing works with

vision (color, motion, form and depth) What if you could not perceive motion?

Hermann Grid (why?)

Theories of Color Vision

Additive color mixing Mixing of lights of different hues Lights, T.V., computer monitors (RGB) Lights add wavelengths

Subtractive color mixing Mixing pigments, e.g., paints Pigments absorb or subtract wavelengths

Color Theory Young-Helmholtz Trichromatic theory Herring’s opponent-process theory Afterimages

Color Vision

Young-Helmholtz trichromatic (three color) theoryRed – Green - BlueMonochromatic

visionDichromatic

vision

Theories of Color Vision Trichromatic theory (Young-

Helmholtz) Three different types of cones

Red Green Blue

Experience of color is the result of mixing of the signals from these receptors

Can account for some types of colorblindness Approximately 10% of men and 1% of

women have some form of “colorblindness” (sex linked trait)

Dichromats: Two colors only Monochromats: One color only

Ishihara Test

Color Vision

Opponent-process theoryThree sets of colors

Red-greenBlue-yellowBlack-white

Afterimage

After image- evidence for the opponent process theory of color vision

.

Stare at the dot in the image below

What do you see (Blink a bit)

Theories of Color Vision Trichromatic theory cannot explain all aspects of

color vision People with normal vision cannot see “reddish-green” or

“yellowish-blue” Red-Green colorblind people can see yellow, which

Helmholtz argues is a result of red and green cones firing – if Helmholtz is correct, how could this be?

Color afterimages? Opponent-process theory (Ewald Hering)

Three pairs of color receptors Yellow-blue Red-green Black-white

Members of each pair work in opposition Can explain color afterimages

Both theories of color vision are valid

Adaptation Dark adaptation

Increased sensitivity of rods and cones in darkness

Light adaptation Decreased sensitivity of rods and cones in

bright light Afterimage

Sensory experience that occurs after a visual stimulus has been removed in response to overstimulation of receptors

Color Vision in Other Species

Other species see colors differently than humans

Most other mammals are dichromats Rodents tend to be monochromats, as

are owls who have only rods Bees can see ultraviolet light Stomatopods have the most complex

color hyperspectral vision in the animal kingdom, allowing them to differentiate between colors that may appear the same to other human and non-human animals.

The Mantis Shrimp is a stomatopod with hyperspectral vision. Hyperspectral capabilities enable the mantis shrimp to recognize different types of coral, prey, or predators.

A question for the ages: How do I know if I am seeing the same

color as someone else? Answer: The wavelength determines

color, so in a properly functioning eye, it will be the same, although color shades can vary significantly and people may name them differently.