Vision

Vision Our most dominating sense (Visual Capture). The eye is like a camera (it needs light).

Phase One: Gathering Light The height of a wave gives us it’s intensity (brightness). The length of the wave gives us it’s hue (color). ROY G BIV The longer the wave the more red. The shorter the wavelength the more violet.

Getting the light in the eye

Structures of the Eye Iris – regulates the amount of light going into the eye (colored part). Pupil – black opening where light enters. Lens – focuses light on the retina. Retina – has layers of sensory cells: Cones – (6 million) for color and daylight vision. Most highly concentrated near the fovea (back center of the eye). Rods – (120 million) for peripheral and night vision. Located along the sides of the retina.

Mnemonic: Really Cool Babies Giggle Obnoxiously (RETINA: Rods, Cones, Bipolar Cells, Ganglion Cells, Optic Nerve)

Foveal Vision To do a test close one eye, fixate on the upper line at the fixation point and try to read the words to the right and left without moving your eyes. Visual acuity decreases with the distance from the fixation point. Foveal vision works like a magnifier, peripheral vision is your data compression.

Vision: In the Brain We have specific cells that see the lines, motion, curves and other features. These cells are called feature detector cells (Discovered by Hubel and Wiesel). Goes to the Visual Cortex located in the Occipital Lobe of the Cerebral Cortex. It’s here that we interpret what we are looking at.

Visual Pathway

Parallel Processing Color Motion Form Depth The processing of several aspects of a problem simultaneously. Color Motion Form Depth

How do we see in color? https://www.youtube.com/watch?v=apmDI1iZUm4

Facts on Color Vision Colors we experience depend on the relative degree of stimulation to the cones. Pigments mixed together absorb more wavelengths than a single pigment (subtractive color mixing) Wavelengths added together stimulate more cones (additive color mixing)

Color Constancy Perceiving familiar objects as having consistent color, even if changing illumination alters the reflected wavelengths. A green apple for instance looks green to us at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red.

What about when the context changes? Because the brain computes the color of an object relative to its context, the perceived color changes. http://www.echalk.co.uk/amusements/OpticalIllusi ons/colourPerception/colourPerception.html

Young-Helmholtz Trichromatic Theory Three types of cones: Red Green Blue These three types of cones can make millions of combinations of colors. Does not explain afterimages or color blindness well.

Hering’s Opponent-Process Theory The sensory receptors come in pairs. Red/Green Yellow/Blue Black/White If one color is stimulated, the other is inhibited.

Color Blindness Types of color blindness: Red / Green (most common) Blue / Yellow Total colorblindness Most colorblind people are dichromats – they lack one kind of photopigment. Males more likely to be colorblind. Missing Red Missing Green Missing Blue

Afterimages

Afterimages When the eyes are then diverted to a blank space, the adapted photoreceptors send out a weak signal and those colors remain muted. However, the surrounding cones that were not being excited by that color are still "fresh", and send out a strong signal. The signal is exactly the same as if looking at the opposite color, which is how the brain interprets it.