Midterm Wednesday and
Thursday
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Multiple Choice
Yes/No and True/False and Matching
Study the lecture notes, textbook
My office hours are after class (NOTE:
I won’t talk about the test material once
students have started taking the test!)
The Visual System
• What kind of energy does the visual
system sense and perceive?
Light
• Light is an oscillation (a wave) in the
electromagnetic field
Properties of light
• What are some characteristics of light
waves?
Properties of light
• What are some characteristics of light
waves?
– amplitude/intensity - how big of a
fluctuation in the field/how many waves
– frequency - how many fluctuations
(waves) pass by a certain point in a
given period of time
– polarization - the orientation of the waves
Properties of light
•What perceptions are associated with
those physical properties?
Properties of light
•What perceptions are associated with
those physical properties?
–Intensity is associated (loosely) with
brightness
–Frequency is associated (loosely) with color
–Polarization isn’t sensed by humans (but it is
by some insects!)
Light
• The spectrum is the range of frequencies of
electromagnetic waves
Using Light
• The eye
– curved
cornea
– lens
– retina
– fovea
– optic disk
Using Light
• Light is focused on the retina by the curvature
of the cornea and the lens
– Flat lens (relaxed muscles) focuses distant points
Using Light
• Light is focused on the retina by the curvature
of the cornea and the lens
– Accomodation: Bulged lens (muscles flexed)
focuses on near points
Using Light
• Light is focused on the retina by the curvature
of the cornea and the lens
• Constriction of the pupil limits how much light
gets in AND reduces the amount of focusing
required of the lens
The Retina has layers of cells
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photoreceptors transduce incoming light
ganglion cells send signals along to the brain
Two kinds of Photoreceptors
• 2 types of photoreceptors: rods and
cones
• rods are very sensitive - useful in dim
light
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