Unit 8 Sensation

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Unit 8 - Sensation
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Outline

• Sensation
• Transduction
• Coding
• Just-Noticeable Difference
• Stevens Power Law
• Signal Detection Theory
• Gustation
• Olfaction

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Sensation

• What is sensation?
• Detection of specific properties of stimuli
• What is perception?
• When the brain uses sensory info to produce a
  response
• Monster example
• Car brake lights

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The 5 senses

• See Vision
• Hear Audition
• Smell Olfaction
• Taste Gustation
• Feel Somatosenses

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Transduction

• Messages transmitted through neural impulses to
  the brain
• Action potentials carried by axons
• Sense organs detect and transmit
• Brain analyzes
• Most senses receptor cells
• Mechanical, thermal, chemical, radiant

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Human capability

• Human Capability
• 7.5 million colors
• 10,000 odors
• 30 20,000 Hz
• 5 main tastes
• Temperature, pressure, pain, balance
• How does an AP code for so many things?

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Coding

• Anatomical which specific nerves of the body
  are firing
• Rubbing your eyes
• Brain surgery
• Temporal rate at which nerves fire
• Determines the intensity of stimulus
• Pressure on skin

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Psychophysics

• The systematic study of the relation between the
  physical characteristics of stimuli and the
  psychological responses (or perceptions) they
  produce. In other words, The physics of the
  mind. p.159

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Just-Noticeable Difference

• JND smallest magnitude of a stimulus a person
  can detect
• Example Comparing weights
• Ratio of 1 in 40
• Can distinguish between 40g and 41g or 80g and
  82g
• Cannot distinguish between 80g and 81g

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JND (cont.)

• Example 2
• White lights ratio is 1 in 60
• Each one of these ratios is the JND for that
  specific stimulus Weber fractions
• Fechners work Figure 6.1
• Contrast with Figure 6.2

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Review Quiz

• T or F Perception is the detection of specific
  properties of stimuli
• False Sensation is the term
• ______ is the process by which sense organs
  convert energy from environmental events into
  neural activity.
• Transduction

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Stevens Power Law

• S kIb
• S is the psychological magnitude
• k is a constant
• I is the intensity of the stimulus
• b determines the shape of the curve
• 0-1 Figure 6.1 (saccharine)
• gt1 Figure 6.2 (salt)

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Saccharine vs. Salt
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Absolute Threshold

• JND Difference threshold
• Absolute threshold smallest detectable stimulus
  intensity
• FYI - Wikipedia
• Vision a candle 30 miles away on a clear night
• Audition a watch ticking 20 feet away
• Gustation 1 teaspoon of sugar dissolved in 2
  gallons water
• Olfaction a single drop of perfume in a
  three-room house
• Somatosenses a bees wing falling a distance of
  1 cm onto a persons cheek

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Signal Detection Theory

• SDT discrimination between a signal (stimulus)
  and noise (combo of background stimuli and random
  nerves firing)
• Response bias tendency to say yes or no when
  you are not sure whether you detected the
  stimulus
• 4 possible judgements

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SDT (cont.)

• What influences response bias?
• Motivation!
• What is a universal motivator that we can use for
  an example?
• Hypothetical example Listening booth
• Condition 1 1 per hit, no penalty for miss
• Condition 2 1 per hit, -0.50 per false alarm
• Condition 3 0.50 per hit, -1 per false alarm
• Condition 4 No reward, -1 for false alarm

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SDT (cont.)

• So
• SDT is less about absolute threshold and more
  about motivation and prior experience

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Review Quiz 2

• T or F As the intensity of the stimulus
  increases, the perceived intensity always
  increases.
• False
• Give an example of a stimulus with a b value
  from 0-1 and a b value gt1. Explain what b
  means.
• Saccharine (.8), Salt (1.3) shape of the curve
  of perceived intensity of the stimulus vs.
  intensity of the stimulus

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Gustation

• Parts of tongue
• Papillae (bumps)
• Taste bud (on papillae)
• Receptor cells (on taste buds)
• Microvilli fills trenches of papillae

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Five Qualities of Taste

• Sourness
• Sweetness
• Saltiness
• Bitterness
• Umami good taste
• Monosodium glutamate

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Taste (cont.)

• Sourness, bitter stay away from tastes
• Sweet, salty, umami eat more tastes
• Umami glutamate an important amino acid
  important for protein

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Olfaction

• Smells play an important role in emotions and
  memory
• Sends information to the limbic system
• Women more sensitive smell than men?
• 10 million receptor cells
• 1000 different receptor molecules to detect
  different odors

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Olfaction (cont.)

• Odor molecules stimulate receptor cells
• Cell becomes excited
• Message passed onto brain by axon
• Cross-modal integration
• Taste is associated with smell
• Smell threshold lower when sweet solution of
  saccharin in mouth

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Primary olfactory system

• Analytical sensory modality can tell individual
  smells
• Example many odors at a carnival
• Key parts
• Olfactory mucosa contain receptor cells
• Olfactory bulbs located at base of brain
  perform first analysis of odors

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Accessory olfactory system

• Pheromones regulate sexual and social behavior
• May effect womens menstrual cycle
• Attraction to the opposite sex

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Main parts of the eye

• Cornea transparent front window, admits
  light, bends light (refraction)
• Pupil constricted in bright light, opened in
  dim light (black part)
• Iris controls the amount of light that enters
  (colored part)
• Aqueous humor watery fluid behind cornea
• Lens focuses light on inner surface of back of
  eye
• Ciliary muscles alter shape of lens to see
  things near or far, called accommodation
• Retina where image is focused interior surface
  of eye

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Eye-problems

• Nearsighted (myopia) image focused in front of
  fovea b/c eye too long concave lens needed to
  correct problem
• Far-sighted (hyperopia) image focused behind
  fovea b/c eye too short convex lens needed to
  correct problem
• Astigmatism image distorted

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Blind spot

• Where optic nerve enters back of eye
• Optic disk where optic nerve exits toward brain
• 130 million photoreceptors all around retina
  except at this spot
• No sensors available to transmit light
• Photoreceptors-gtneurons-gtaxons-gt
• optic disk-gtoptic nerve

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Modern eye surgeries

• Radial Keratotomy Photorefractive Keratectomy
  (RK PRK)
• RK knife and cut slits in cornea to change its
  shape
• PRK stoma, or middle layer of cornea vaporized
  w/ laser top layer scraped away
• LASIK same thing, but cuts slit through top
  layer of cornea (epithelium)
• Thermokeratoplasty heat to reshape cornea,
  different kind of laser used
• Orthokeratology contact lenses and ring segment
  that are inserted in stroma

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Pathway of light in retina

• Photoreceptors?Bipolar cells?Ganglion cells?Brain
  
• Bipolar cells neurons that form synapse with
  photorecptors
• Ganglion cells axons travel to optic nerve
• Optic nerve travels to brain
• Interconnecting neurons

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Rods and Cones

• Two types of photoreceptors
• 125 million rods, 6 million cones
• Rods good in dim light extremely sensitive to
  light, but not colors
• Cones see colors, but need good light\
• Fovea contains only cones, color vision
  central, most detailed vision

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Rods and Cones (cont.)

• Number of rods increases as distance increases
  from the fovea
• Up to 100 rods transmit info to one ganglion cell

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Bleaching process

• Photopigments 1 kind for rods (Rhodopsin), 3
  for cones
• 1000s of photopigment molecules in photoreceptors
• Light strikes and splits into two molecules
• Bleached
• Start of transduction
• Starts the transmission to the brain
• Energy cause molecules to recombine

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Adaptation to Light and Dark

• Dark adaptation takes your eyes a few minutes
  to adjust to the dark
• Could be temporarily blind
• Happens because Rhodopsin is slow to regenerate
  after being bleached
• Takes approximately 20-30 minutes for Rhodosin to
  completely regenerate
• Light adaptation
• Only takes about a minute
• Contrast sensitivity low
• Why?

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Low contrast sensitivity
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Light Sensitivity Chart

• http//www.yorku.ca/eye/toc.htm

http//www.yorku.ca/eye/toc.htm
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Eye movements

• Conjugate movements control for distance
  (focus)
• Saccadic movements jumping movements (reading)
• Pursuit movements tracking objects (hitting a
  baseball)

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Physical and Peceptual Dimensions of Color

• Hue (color) phys characteristic wavelength
• Brightness phys char intensity
• Saturation phys char purity
• Ex. Pure red or pure blue
• Compare w/ white light

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Adding and subtracting colors

• Light is synthetic we add different wavelengths
  to form white light
• Can break apart w/ prism
• When mixing paint, adding two colors together is
  really subtraction
• Adding wavelengths always loses color
• Taking away wavelengths always gains color

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Opponent process theory of color

• Why is it hard to imagine a greenish red or a
  yellowish blue?
• Red/green and Yellow/blue ganglion cells
• Both fire at same rate when not stimulated
• Red light-gtRed cone (excited)-gtRed/Green ganglion
  cell fires faster
• Green light-gtGreen cone (excited)-gtRed/Green
  ganglion cell fires slower
• Works the same for Yellow (excited)/Blue
  (inhibited) ganglion cells

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Figure 6.17 Breakdown

• Red light triggers red cone-gt red/green
  ganglion cells (excites)
• Green light triggers green cone-gt red/green
  ganglion cells (inhibits)
• Yellow light triggers red green cones
• -gtYellow/blue ganglion cells (excited)
• Blue light triggers blue cones-gt Yellow/blue
  ganglion cells (inhibited?)

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Negative Afterimages

• Rebound effect ganglion cells that are excited
  or inhibited for a prolonged period of time, fire
  either faster or slower
• Contingent aftereffects Figure 6.19

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Color blindness

• Protranopia red cones with green photopigment
  (1 in 20 males, sex-linked)
• Deuteranopia green cones with red photopigment
• Tritanopia Yellow/blue system loss of the blue
  cone causes world too be seen as greens and reds

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Audition

• Sound measured in Hz (cycles/sec)
• 30 Hz to 20,000 Hz
• Sound Pressure changes in the air
• Molecules of air are compressed or rarefaction

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Parts of the Ear

• Pinna outside ear
• Eardrum (tympannic membrane) thin flexible
  membrane, vibrates and passes to receptor cells
• Ossicles hammer, anvil, stirrup (malleus,
  incus, and stapes) transmit vibrations to
  fluid-filled inner ear
• Cochlea contains fluid, two windows (round and
  oval), and basilar membrane
• Basilar membrane contains auditory receptor
  cells

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Basilar Membrane

• Stirrup presses against membrane behind oval
  window
• Pressure changes in fluid cause membrane to
  vibrate
• High-freq sounds cause end of membrane near oval
  to vibrate
• Med-freq sounds cause middle of vibrate
• Low-freq sounds cause tip to vibrate
• Round window moves fluid in and out

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Auditory hair cells

• Turn mechanical energy into neural energy
• Cilia ends embedded in tectorial membrane
• Sound cause cilia to vibrate
• Electrical charge altered across cell membrane

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Pitch

• Pitch frequency
• Axons cannot fire rapidly enough to code
  high-freq sounds
• Code for high and medium sounds by location on
  basilar membrane (anotomical coding)
• Low-freq sounds (below 200 Hz) basilar membrane
  vibrates in synchrony with sound waves (temporal
  coding)

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Loudness

• Temporal coding Axons fire more rapidly to
  indicate to increase intensity
• Low-freq Louder sound means more hair cells

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Timbre

• Distinctive combination of harmonics and
  fundamental frequency (basic pitch of sound)
• Harmonics multiples of fundamental frequency
• Synthesizing sounds produces complex frequecies
• Ear analyzes all these frequencies to hear the
  complexity of a sound

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Sound Location

• Determined by relative loudness and difference in
  arrival time
• Relative loudness
• Sound shadow casted by solid objects
• Damps out sound
• Difference in arrival time
• One eardrum pushed in while the other pulled out
• Axons fire at different times
• Sound has aftereffects like vision

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The Somatosenses

• Skin does not have sensory receptor cells
• Dendrites of neurons start transmition of info to
  brain
• Skin and inner ear sense 4 different qualities
  temperature, pain, pressure, and balance

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Temperature

• The change in temperature is the important info
  signaled to the brain
• One hand in hot water, one in cold and then into
  luke warm
• Hand that was in hot water feels cold
• Hand that was in cold water feels hot
• Extreme heat/cold are exceptions

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Pressure

• Constant pressure on skin will not be felt if
  there is no change
• Similar to perceptual fading that happens in
  vision
• Two point discrimination method technique to
  measure sensitivity
• Lips and fingertips most sensitive
• Caliper used to measure

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Pain

• Two aspects of pain sensory aspect and
  emotional aspect
• Sensory aspect Opiates (morphine) block
  transmission of pain info to brain by stimulating
  receptors
• Emotional aspect Tranqulizers (valium) block
  emotional reaction
• I feel the pain, it just not bother me.
• Pain is a great motivator
• Important survival mechanism
• Phantom limbs
• Wired to feel pain in all 4 limbs, even if they
  were never there

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Vestibular System

• Balance system of inner ear
• Semicircular canals changes in rotation of head
• Vestibular sac calcium carbonate crystals shift
  and move cilia on hair cells
• Keeps things from moving around while we are
  walking