Vision EYE 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

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 Eye The Retina  Rods and Cones Rods Cones

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 Eye The Retina  Optic nerve  Blind spot  Fovea

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

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) theory  Red – Green - Blue  Monochromatic vision  Dichromatic 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 theory  Three sets of colors  Red-green  Blue-yellow  Black-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.