Syllabus Course Schedule - Buena Vista University

Syllabus pdf file Course Schedule

Structure of the eye and retina

Chaper 3: Intro to Vision http://web.bvu.edu/faculty/ferguson/Course_Material/2011_Courses/Perce...

1 of 10 3/6/2012 1:06 PM

In-class demo: do Virtual Lab activity 3-6 (Visual Path in the Eyeball)

Focusing, changes with age and correction

Some important terms:

hyperopia/presbyopia (farsightedness because of age...image is focused behind theretina)myopia (nearsightedness...image is focused in front of the retina)LASIK...surgery on the cornea, not the lens.Cataract...clouded lensGlaucoma...increased intra-ocular pressure in aqueous humor

Visual receptors and transduction


2 of 10 3/6/2012 1:06 PM

What does the work of Hecht et al (1942) tell us about the diagram above?

Dark adaptation


3 of 10 3/6/2012 1:06 PM

Be ready to describe the general procedure for producing the blue curve above.How would you have to modify the procedure to get the yellow curve?

Rods & cones

Some basic facts about the retina:


4 of 10 3/6/2012 1:06 PM

each retina has a blind spot, located 10-15 degrees below and medial to the fovea.~120M rods~6 M conesrods have much lower absolute thresholds than conesfovea contains only conesperiphery has mostly rods, some conesconcentration of rods is greatest ~15 degrees from foveathree types of cones, each maximally sensitive to a different wavelength (R, G, B)the overall spectral sensitivites of rod and cone vision are different:

How does the information above explain the following:It's a dark, clear summer night and you've been outside long enough to be fully dark adapted. As you look at the sky, you see a dim star in the corner of your eye. When you look directly at itto see it better, it disappears, but reappears when you look away again.Even though each retina has a blind spot, we don't continually see two blank areas in our visualfield.Highway workers wear those ugly yellow-green vests.You are sitting on your porch one summer evening and, as the sun goes down, you notice thatthe red roses, which were so beautiful a few minutes ago, are quickly losing their color and nowjust look dark. The green grass and blue flowers, however, seem to be staying bright andcolorful a bit longerWhen measuring your visual acuity (ability to see fine details), your eye doctor asks you to lookdirectly at the letters on the wall.

Neural convergence in the retina

The diagrams below are highly schematized versions of Fig. 3.25 in the text.


5 of 10 3/6/2012 1:06 PM

In-class demo: do Virtual Lab activities 3-7 & 3-8

A couple of addional facts:each retina contains ~126M receptors (rods + cones)each optive nerve contains ~1M fibers (axons from ganglion cells)thus, on average, convergence must be ~ 126:1convergence is minimal in fovea but increases significantly in periphery to a max of ~5000:1the cones, highly concentrated in each fovea, giving rise to about 40% of the 1M fibers (axons)the the optic nerve. This means the fovea has disproportionately large representation in thebrain:

Based on the information above, be ready to explain the following:When measuring your visual acuity (ability to see fine details), your eye doctor asks you to lookdirectly at the letters on the wall.Complete the demonstration found HERE. Were the letters easier to read in trial 1 or trial 2? Why?


6 of 10 3/6/2012 1:06 PM

Color Vision: a two-part story.

Part 1: three types of cones

Part two: two types of opponent-process ganglion cells & cells in the thalamus:

How to resolve this:


7 of 10 3/6/2012 1:06 PM

Lateral Inhibition

Lateral inhibiton simply refers to the fact that when one receptor in the retina fires, it tends to inhibitthe firing of other nearby receptors. Here are a couple of additional bits of info:

The faster a receptor fires, the greater the inhibition on nearby receptorsInhibition decreases with distance.

Here's how the text explains this phenomenon:

What should happen if we were to move the light from receptor B to C?

In-class demo: Virtual Lab activity 3-9

Remember the image below, from the text? What do you suppose it has to do w/ lateral inhibition?


8 of 10 3/6/2012 1:06 PM

Look carefully at the two center gray bands and describe how they appear. Does each band lookuniformly gray across it's entire width?

Lateral inhibition and mach bands produce distortions in the way we see the world. Can you think of


9 of 10 3/6/2012 1:06 PM

why this might be useful? [Hint: think about seeing edges.]

Here, on the other hand, is an example of the distortions from lateral inhibition interfering withperception:

And how about this example of simultaneous contrast:


10 of 10 3/6/2012 1:06 PM

Syllabus Course Schedule - Buena Vista University

Documents

Transcript of Syllabus Course Schedule - Buena Vista University