VI. SENSATION

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VI. SENSATION
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Two pieces of the puzzle....

• The nervous systems 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 ones 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 (retinas 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 arent 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
• - havent 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.