vi. sensation. two pieces of the puzzle.... the nervous system’s job is to coordinate us with our...
TRANSCRIPT
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VI. SENSATION
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Two pieces of the puzzle....
• The nervous system’s job is to coordinate us with our environment.– Electric-chemical process
• We are exposed to an enormous amount of stimuli.– To deal with this, our perceptions can be
biased.
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A. What is sensation?
• How does physical energy from the environment get encoded as neural signals?
• 1. Sensation: process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.
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A. What is sensation?
• 2. Sensation vs. Perception• Sensation is not all we require to make sense of
world (“to see the bear”)• Sensation: detecting physical energy....• Perception: How we select, organize, and
interpret the information we sense.– Active process, involves imposing order on stimuli– Sensation provides “raw” information (stimuli) that is
selected, organized, etc.
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B. Basics of Sensation:
• 1. 5 senses
• Seeing
• Hearing
• Smelling
• Tasting
• Touching
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B. Basics of Sensation:
Sensation involves converting one type of energy into another.
- Energy from environment – to neural impulses.• i. External Stimulus (energy) – big, furry, smelly bear • ii. Stimulus takes different energy forms...
– see bear: light waves...
• iii. That energy interpreted by receptors.– see bear: light waves received by photoreceptors in retina
• iv. Convert that energy into form brain can understand.
2. Transduction: Stimulus is converted into neural impulses
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C. What do we sense/detect from the environment?
• We do not detect all of the stimuli that are present.
Examples?
• Senses are limited or restricted.• 1. Absolute Threshold: The minimum
stimulation necessary to detect a particular stimulus. (usually 50% of time)
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C. What do we sense from the environment?
• How do we determine absolute threshold?• 2. Signal Detection Theory:
Used to predict how & when we will detect a stimulus.Considers:– Strength of signal
Absolute thresholds vary – not inherent to the stimulus.– Situational differences (expectations, motivation, fatigue)– Individual differences (experience)
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C. What do we sense from the environment?
• 3. Sensing the difference between 2 stimuli:• Difference threshold (just noticeable difference):
Minimum difference a person can detect between any two stimuli (50% of the time)– How to detect the JND?
• right or wrong• adjustment
– The JND increases with the magnitude of the stimulus.
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C. What do we sense from the environment?
• 4. Can we ever detect stimuli that are below threshold?
Subliminal: below one’s absolute threshold for conscious awareness.
• How do we test for this?– Yes – can detect stimuli under threshold.
– Yes – can have subtle, fleeting influence on thinking.
– No – does not have powerful, enduring effect on behavior.
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C. What do we sense from the environment?
• 4. What else influences our sensitivity to stimuli?• Sensory Adaptation: diminishing sensitivity to an
unchanged stimulus.
- after constant exposure to a stimulus, our nerve cells fire less frequently.
• But...
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• Why?
• Our eyes are always quivering just enough to maintain stimulation of neurons.
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D. VISION
• Review the basic process: Stimulus input (“bear” or beautiful sunset) Input as light waves Received by receptors in eye. Light waves transformed into neural
information – impulses (transduction). Messages go to brain to be
organized/interpreted - to where in brain?
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D. VISION
• 1. What is the stimulus input?
a. Light waves or energy.
- Pulses of electromagnetic energy that our
visual system experiences as color.
- Do we see all possible light waves?
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D. VISION
• 1. What is the stimulus input?
What determines the characteristics of the colors we see?– a. Wavelength: Distance from one wave peak to
another.
– Determines “hue” or color.
– b. Amplitude: Wave height.
– Determines amount of energy in light wave or intensity/brightness.
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D. VISION
• 2. The process of light energy becoming vision.
a. Structure of the eye – key are the receptors.
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D. VISION
• a. Important Structures:
• cornea: transparent protector. pupil: adjustable opening, determines
how much light is let into eye. lens: focuses incoming rays into an
image on retina. retina: light sensitive tissue - receptors.
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D. VISION• b. Accommodation
Process by which lens changes shape to focus the image of objects on retina.
c. Receptors in retina
- When image focused onto retina by lens: upside down.
- Key to vision: light energy neural impulses
Light strikes receptors in retina produces chemical changes (photopigments that break down)
trigger neural impulses.
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D. VISION• c. Receptors (2 types):
Rods: located in peripheral area of retina.– Highly sensitive to light.
– Enables black and white vision.
Cones: located in fovea (retina’s central point of focus).– Each cone has cell that relays messages directly to visual cortex
– Detects fine detail from light energy.
– Enables us to see color.
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Retina processes some info before gets to brain (encodes and analyzes it)
Chemical reaction – activates bipolar cells – eventually activates ganglion cells that make up the optic nerve.
Info. sent to brain through optic nerve - brain rearranges image to right side-up.
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D. VISION
When info. reaches visual cortex, processed by feature detectors.
• d. Feature Detectors:Neurons in brain that respond to specific features of
the stimulus (shape, angles, movement).• Importance of “brain” in vision:
– “parallel processor”
• e. Comparing the vision process to other senses...
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D. Vision
• 3. Color Vision• Light rays themselves aren’t “colored”• Color of an object is the wavelength “rejected” or reflected
(versus the others that are absorbed)
• a. Young-Helmotz Trichomatic Theory• Retina - cones that are sensitive to 3 colors:
– red, green, blue– each contain different photopigment– fires differently depending on wavelength struck by– relationship to colorblindness?
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D. Vision
• 3. Color Vision• After-images – why?• b. Opponent-Process Theory• Neurons are sensitive to “pair of opponent” colors:
– red/green, blue/yellow, black/white
– stare at green – remove green stimulus – cell is fatigued – leaves only “opponent” color part of cell to fire – red
– also explains why color blind people can see yellow
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D. VISION
• 4. Why do some people have poor vision?
a. Acuity: sharpness of vision.
Poor vision: Caused by small distortions in shape of eye ball.
b. Nearsightedness: eyeball is longer than normal in relation to lens.
b. Farsightedness: eyeball is shorter than normal in relation to lens.
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• Sensation:- haven’t touched on organizing/interpreting that material (perception)- “raw” material for perception- started at “entry level”, data driven
“bottom-up processing”• Perception: “top-down processing”
- concept driven, use preexisting knowledge to interpret information.