CLASS PREVIEW
*Describe the process of visual transduction and how the brain constructs visual perceptions
*Continue Unit Ib (“Sensation: Vision” (M 1.6b))
AP PSYCHOLOGY DAY 17
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
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UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*Research shows that while our senses are very acute, they do have their limits.
-The difference threshold is the minimum difference between two stimuli required for detection 50% of the time; aka the just noticeable difference (JND)
**Weber’s Law (Weber-Fechner Law) is the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)
--Add 1 ounce to a 10-ounce weight, you will detect the difference; add 1 ounce to a 100-ounce weight and you will not (?)
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*Sensory adaptation is diminished sensitivity to a stimulus as a consequence of constant stimulation; ex. Do you feel your shoes all day?
-When constantly exposed to an unchanging stimulus, we become less aware of it because our nerve cells fire less frequently
-All of our senses (taste, touch, smell, hearing), except VISION, experience sensory adaptation (?)
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*Our eyes receive light energy (pulses of electromagnetic energy) and transduce (transform) it into neural messages
-Light travels in waves, and the shape of those waves influences what we see:
**Light’s wavelength (the distance from the peak of one light wave (or sound wave) to the peak of the next) determines the hue (the dimension of color; “ROY G BIV”)
--“A red shirt reflects red light and absorbs other colors.”
--“Objects appear black because they absorb all colors and white because they reflect all wavelengths of light.”
**A light wave’s amplitude, or height, determines its intensity (the amount of energy in a light wave (or sound wave) (“brightness”; “loudness”)
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*When we look at something, we turn our eyes toward the object and the reflected light coming from the object enters our eye:
A. Light enters the eye through the cornea (the eye’s clear, protective outer layer, covering the pupil and iris)
B. The light then passes through the pupil (the adjustable opening in the center of the eye through which light enters)
**Surrounding the pupil and controlling its size is the iris (a ring of muscle tissue that forms the colored portion of the eye)
C. Light then hits the lens (the transparent structure behind the pupil that changes shape to help focus images on the retina, a process called accommodation)
****The light that hits the eye has been inverted by the lens (?)
D. Light rays are focused on the retina (the light-sensitive back inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information)
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*When light hits the retina, buried photoreceptor cells, the rods and cones, trigger a chemical response
-Rods are retinal receptors that detect black, white, and gray, and are sensitive to movement
**Rods are necessary for peripheral and twilight vision, when cones don’t respond
-Cones are retinal receptors that are concentrated near the center of the retina (the fovea, or central focus point in the retina) and that function in daylight or well-lit conditions
**Cones detect fine detail and give rise to color sensations
-Activation of rods & cones will cause the activation of the bipolar cells, which will cause the activation of the ganglion cells, whose axons twine together like strands of rope to form the optic nerve (the nerve that carries bureau impulses from the eye to the brain)
**The blind spot is the point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there
**The optic nerve sends these impulses to the lateral geniculate nucleus (LGN) region of the thalamus (?), before the before sent to the visual cortex of the occipital lobe
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*Question- If no one is in the room to see it, is the tomato red?
-NO!
**First, the tomato is everything but red, because it rejects (reflects) the long wavelengths of red
**Second, the tomato’s color is our mental construction… “The [light] rays are not colored”- Sir Isaac Newton (1704) (?)
*Most researchers agree that a combination of two theories is is needed to explain the phenomena of color vision:
A. The Young-Helmholtz Trichromatic (3-Color) Theory is the theory that the retina contains three different types of color receptors (red-green-blue) which, when stimulated in combination, can produce the perception of any color
B. The Opponent-Process Theory is the theory that opposing retinal processes (red-green, blue-yellow, white-black) enable color vision
**Some cells are stimulated by green and inhibited by red; other cells are stimulated by red and inhibited by green
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*In the visual cortex (occipital lobes), the visual impulses from the retinal cells activate the feature detectors (discovered by David Hubel and Torsten Wiesel) which are nerve cells that respond to specific features of the stimulus, such as shape, angle, or movement
-Parallel processing allows for the features to be processed simultaneously
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*Complete the DAY 17 EXIT TICKET assignment posted to the Google Classroom!!!
UNIT 1: BIOLOGICAL BASES OF BEHAVIOR
*Continue Unit 1b (“Sensation: Hearing” (M 1.6c)”)
*NONE!!!