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Our eyes receive light energy and __________
transduces it
into neural messages that our brain processes
into what we consciously see.
• When we look at
things, we actually
see the light
reflected off of them.
• Visible light is a thin
slice of the whole
spectrum of
electromagnetic
energy.
Light and sound use similar descriptive language
because both have properties of waves:
● wavelength
● amplitude
(color)
(intensity)
The Structure of the Eye
The Structure of the Eye
Cornea = outer covering of the eye.
The Structure of the Eye
Pupil = the adjustable opening in the center of the eye through
which light enters.
The Structure of the Eye
Iris = a ring of muscle tissue that forms the colored portion of the
eye around the pupil and controls the size of the pupil opening.
• The iris dilates/constricts in response to changing light intensity
The Structure of the Eye
Lens = the transparent structure behind the pupil that changes
shape to help focus images on the retina.
The Structure of the Eye
Retina = the light-sensitive inner surface of the eye, containing the
receptor rods and cones plus layers of neurons that begin the
processing of visual information.
The Structure of the Eye
Blind Spot = the point at which the optic nerve leaves the eye,
creating a “blind” spot because no receptor cells are located there.
The Structure of the Eye
Fovea = the central focal point in the retina, around which the
eye’s cones cluster.
The Structure of the Eye
Optic Nerve = the nerve that carries neural impulses from the eye
to the brain.
The Retina’s Receptor Cells
• Rods
 Detect black, white, and gray; necessary for
peripheral and twilight vision.
• Cones
 Concentrated near the center of the retina
and function in daylight or in well-lit
conditions. The cones detect fine detail
and give rise to color sensations.
The Retina’s Receptor Cells
Cones
Rods
The Retina’s Receptor Cells
The Retina’s Reaction to Light
• Eyes are important organs in your sight
brain
process, but you see as much with your _____
as you do your eyes!
Assignment:
Complete the Eye Sensation handout
• It is due tomorrow.
There will be a quiz over this tomorrow.
Visual Information Processing
• Feature Detector Cells
– Specialized neurons in the brain that
respond to specific features, such as shape,
angle, or movement.
– Get their name from the ability to respond
to specific features
– Pass information to teams of cells (supercell
clusters) that respond to specific features.
fMRI scans show different activation areas.
Research indicates we have a “vast visual
encyclopedia” of specialized cells that respond to
one type of stimulus.
Visual Information Processing
• Parallel Processing: the brain divides stimuli
into subdivisions
– Motion
– Form
– Depth
– Color
• The brain processes these in separate cortex
areas, then our perceptions are formed by
them being integrated together.
Parallel Processing: the brain divides stimuli into
subdivisions
Parallel Processing: the brain divides stimuli into
subdivisions
Parallel Processing: the brain divides stimuli into
subdivisions
Parallel Processing: the brain divides stimuli into
subdivisions
Parallel Processing: the brain divides stimuli into
subdivisions
A simplified summary of
visual information processing
Scene
Retinal
Processing:
Receptor rods
and cones:
transduction
Feature Detection:
Brain’s detector cells
respond to specific
features – edges, lines,
angles
Parallel Processing:
Recognition:
Brain cell teams process
combined information
about motion, form,
depth, color
Brain interprets the
constructed image
based on
information from
stored images
Color Vision
• Young-Helmholtz Trichromatic theory
– Theory that the retina has three different color
receptors: red, green, and blue.
Color-Deficient People
• Most are not truly “colorblind”
• Lack functioning in red or green sensitive
cones (sometimes both)
• Their vision is monochromatic or dichromatic
instead of trichromatic.
Color Vision
• Opponent-Process theory
– Theory that vision has four primary colors
arranged in pairs: red and green, blue and yellow
– If one in the pair is stimulated, the other cannot
be working.
Stare at the white dot for 30 seconds
Which theory is correct?
• Probably both are correct.
• Two-stage color processing
– RGB cones respond to different stimuli
– These signals then processed by the nervous
system’s opponent-process cells.