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The Visual Process
Mr. KochAP Psychology
Forest Lake High School
The Visual Process• Transduction
• the process by which our sensory systems convert stimulus energy into neural messages
1. Wavelength• The distance from one wave peak to
the next
2. Hue• The color we experience
(determined by wavelength)
3. Amplitude• Height of the wave peak
4. Intensity• Amount of energy in light waves,
influences brightness (determined by amplitude)
Iris
Cornea
Pupil
LensRetina Fovea (point of
central focus)
Blind Spot
Optic Nerve
Pupil - small opening which allows light to enter.Iris – a colored muscle that surrounds and dilates or constricts the pupil (regulates amount of light entering)
Lens – focuses the incoming rays by changing its curvature (called accommodation)
Retina – the light-sensitive surface on which the rays focus – the multilayered tissue that lines the inside of the back of the eyeball
*Note: the retina has many receptor cells which convert the inverted image (light energy) into neural impulses. When sent to the brain, these neural impulses are reassembled to create a perceived, upright-seeming image.
The Retina
• Light travels through outer cells to buried receptor cellscalled rods and cones.
• The rods and cones generate neural signals to alert the next layer of cells called the bipolar cells.
• The bipolar cells activate the ganglion cells, whose axons converge like strands of rope to form an optic nerve that carries information to the brain.
• Where the optic nerve leaves the eye there are no receptor cells, creating a blind spot.
• The fovea is where the cones are clustered, the retina’s area of central focus (no rods).
Rods vs. Cones
Rods• Do not have their own bipolar
cells, they share with other rods.
• No color.• Remain sensitive in dim light,
takes about 20 minutes to adjust
• 120 million• Periphery of retina• High sensitivity in dim light –
help see in the dark.
Cones• Many have their own bipolar
cells – aids in precise info and detection of fine detail.
• Color vision• Do not respond in dim light
(can’t see colors in dim light)• 6 million• Center of retina• Low sensitivity in dim light
Visual Information Processing• Feature Detectors
• Certain cortical neurons which receive visual info and respond to only certain features of a scene
• Parallel Processing• The brain’s capability to process visual components
simultaneously (i.e. a face as opposed to an eye, a nose, etc.) – it breaks vision down into sub-dimensions such as color, depth, movement, and form
Color Vision– We can discriminate 7 million different shades!– 1 in 50 people are “color-deficient”
(esp. males – genetic)
• Young-Hemholz Trichromatic Theory– The retina has 3 types of color receptors – each sensitive to
red, green, or blue. When we combine these, we get all the other colors
• Herring: afterimages – Opponent Process Theory– After leaving the receptor cells, visual information is
analyzed in terms of opponent colors • Red/Green; Blue/Yellow; Black/White
– White contains all colors in spectrum
Color Vision• Summary– The retina’s red, green, and blue cones respond in
varying degrees to different stimuli; their signals are then processed by the nervous system’s opponent-process cells en route from the thalamus to the visual cortex
• Color Constancy– Perceiving familiar objects as having consistent
color, even if changing illumination alters the wavelengths reflected by the objects• Perception of color is influenced by the context