Vision

Agenda 1. Bell Ringer: How can you target location by sound alone? 2. Notes: Vision (20) 3. Vision Brain Games (15) 4. Vision and balance Experiment (15) 5. Color Experiment (10) HW: Work on twitter posts

A.    Begins with light entering the eye human photoreceptors – the most sensitive to WAVELENGTHS of energy called visible spectrum visible spectrum ranged from RED to VIOLET

Characteristics of light WAVELENGTH - corresponds to perceptual term hue or COLOR INTENSITY - corresponds to perceptual term BRIGHTNESS COMPLEXITY/ PURITY - corresponds to perceptual term SATURATION which is determined by a mixture of wavelengths

Wavelength (Hue) Hue (color) is the dimension of color determined by the wavelength of the light. Wavelength is the distance from the peak of one wave to the peak of the next.

Different wavelengths of light result Wavelength (Hue) Violet Indigo Blue Green Yellow Orange Red 400 nm 700 nm Short wavelengths Long wavelengths Different wavelengths of light result in different colors.

Intensity (Brightness) Intensity Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.”

Brain Games – The eye http://www.youtube.com/watch?v=lmfHdB-s7S8

retina pupil lens fovea optic nerve to visual cortex iris cornea Blind spot

C. Structures of the eye SCLERA - mostly “white” part of the eye which provides protection from injury and structure CORNEA - specialized, transparent portion of the sclera through which light enters IRIS - pigmented muscle that gives the eye its color and regulates the size of the pupil

PUPIL - opening in the iris that reduces glare LENS - transparent shape changing convex structure that focuses images on the retina; it changes shape to bring objects into focus

The Lens Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

In the eye of a person with _______________ vision, the light rays from distant objects focus ______________ the retina. When their image reaches the retina, they rays are ______________, blurring the image. Rays of light converge on the retina of a ______ eye. This occurs for both nearby objects, and with appropriate readjustments in the curvature of the lens, for objects far away In the eye of a person with ____________vision, the light rays from nearby objects come into focus ____________the retina, resulting in blurred images. nearsighted farsighted normal in front of behind spreading out

RETINA - layer containing photoreceptors, rods, and cones that transduce light energy to electrochemical energy; operates like film in a camera RODS - located in the retina’s periphery, these are capable of receiving light energy in low light but are unable to detect color (sensitive to black, white, and gray) and functions in night vision CONES - located in the middle of the retina to detect color in brighter light and functions in the day time both rods and cones synapse with bipolar cells and ganglion cells

Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

FOVEA - minute area in the center of the retina where vision is shaped; the point of central focus

OPTIC NERVE - nerve that leads out of the eye toward the brain carrying information about light BLIND SPOT - location on the retina where the optic nerve leaves the eye on its way to the brain

Visual pathways 1. OPTIC CHIASM - junction of the two optic nerves where fibers from nasal sides of the two retinas cross; point at which approximately two-thirds of the fibers that make up the optic nerve cross over the midline of the brain 2. VISUAL CORTEX- located in the occipital lobe of both hemispheres which contains the many specialized cells for visual perception

FEATURE DETECTORS - nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement SHAPE DETECTORS - Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.

Visual Information Processing PARALLEL PROCESSING- Processing of several aspects of the stimulus simultaneously. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc. OBJECTIVE 8| Discuss parallel processing and discuss its role in visual processing.

Color theories Young-Helmholz trichomatic theory: a. three different kinds of cones respond to only RED, BLUE, GREEN b. “other colors” are perceived by the mixing of signals in the cones c. theory is used to explain COLOR BLINDNESS but not afterimages - most common colorblindness is caused by a malfunction in the GREEN cone system complete colorblindness is rare

Photoreceptors Blue Cones Green Cones Red Cones MacNichol, Wald and Brown (1967) measured directly the absorption spectra of visual pigments of single cones obtained from the retinas of humans. Short wave Medium wave Long wave

Ishihara Test

Color perception Subtractive color mixing works by REMOVING some wavelengths of light, leaving less light. Additive color mixing works by putting MORE light into the mixture than any one light.

Opponent process theory by EWALD HERING two color process which is RED verses GREEN perception and one for YELLOW verses BLUE perception In the THALAMUS, some neurons are turned on by red but off by green. This helps to explain afterimages. - an afterimage is when you look at red long enough, a GREEN after image will appear or if you look at YELLOW long enough a blue after image will appear

Gaze at the middle of the flag for about 30 seconds. When it disappears, stare at the dot and report whether or not you see Britain's flag.

Color Constancy Color of an object remains the same under different illuminations. However, when context changes the color of an object may look different. OBJECTIVE 10| Explain the importance of color constancy. R. Beau Lotto at University College, London