Vision- How do we see what we see?

Vision Purpose of the visual system transform light energy into an electro-chemical neural response Represent characteristics of objects such as- size, color, shape, and location

Step One: Gathering Light Light is reflected off objects & gathered by eyes 2)Light Waves : Vary in: perceptions: Amplitude (height) Brightness Wavelength Color (hue) Fill is opject cahracteritics= discuss paralell process

Wavelength in nanometers (billionths of a meter) Wavelength to longest to shortest red ,orange yellow, green blue, indigo , violet Gamma rays X-rays Ultra- violet Infrared Radar Broadcast bands AC circuits Visible light Prism White light 400 500 600 700 10 -5 -3 -1 1 3 5 7 9 11 13 15 17 Wavelength in nanometers (billionths of a meter)

Step Two: In the Eye

Cont…

STEP THREE: IN THE BRAIN Retina Optic tract chiasm nerve Visual area of the thalamus Visual cortex

How do I remember it all? Cool People in line rarely cut, real blonde girls flirt Cornea…Pupil…Iris…Lens…Retina…Cones…Rods…. Bipolar cells Ganglion Cells….Feature Detectors

Additive Color Mixture Combining lights of different wavelengths =the perception of new colors Examples: red + green = yellow red + blue = purple

Trichromatic Theory of Color Vision Mixing three primary lights= experience of all possible colors (Young and Helmholtz)

Complementary Afterimages http://www. psychologie. tu-dresden After staring at this image for about 3 minutes a red white and blue afterimage should be seen. To do this the students must be led to stare at the fixation point in the green flag for 3 minutes without moving their eyes. This is difficult to do but critical to the demo which is based upon the green flag falling on the same retinal location until fatigue of the cone pigments occurs. After the adaptation period have the students refixate on the white screen. They should see a red white & blue flag. Ask them how this can be explained from the viewpoint of trichromatic theory. It cannot and requires an opponent process theory. Yet trichromaticity is an accepted theory of the retina. Therefore this kind of afterimage must reflect properties of post-retinalstructures, and in fact the opponent processes illustrated by this demo arise in the ganglion cells that form the head of the ooptic nerve.

Opponent-Process Theory ( an antagonistic process) Herring proposed that we have two types of color opponent cells red-green opponent cells blue-yellow opponent cells

Video Clip- Blue man http://youtu.be/W-yLfm5HsHc

Overview of Visual System The eye is like a camera, but instead of using film to catch the light we have rods and cones Cones allow us to see fine spatial detail and color, but can not function well in dim light Rods enable us to see in dim light, but at the loss of color and fine spatial detail Our color vision is based on the presence of 3 types of cones, each maximally sensitive to a different range of wavelengths

Visual information is processed by ganglion cells ________ it is processed by rods and cones and ________ it is processed by bipolar cells. a. before; after b. after; before c. before; before d. after; after

The opponent-process theory is most useful for explaining one of the characteristics of: a. phantom limb sensations. b. prosopagnosia. c. Weber's law. d. accommodation. e. afterimages

Demo: Additive Color Mixing http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=11

Color Mixing Two basic types of color mixing subtractive color mixture example: combining different color paints