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VI. SENSATION

VI. SENSATION

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VI. SENSATION. 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. A. What is sensation?. - PowerPoint PPT Presentation

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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 signalAbsolute 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.