Sensation

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Sensation Perception

• Chapter 5

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• Sensation

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Sensation

• Refers to how our sense organs respond to and
  detect external stimulus energy (e.g. to lights,
  air vibrations, odors, and so on), and how those
  responses are transmitted to the brain.
• In summary

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Sensation

• Is done by sensory receptors
• Sensory organs code sensory stimulation so that
  the brain can understand them
• This is called

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SensationSensory Receptor Cells
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Sensation

• First, receptors receive
• Then,
• This is called
• Next, connecting neurons in the sense organs

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Sensation

• Transduced messages carried by nerve impulses to
  the brain, are called
• Two types of Sensory Coding
• Quantitative
• Qualitative

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SensationQuantitative Sensory Coding

• For quantitative factors,
• Is characterized by the

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SensationQualitative Sensory Coding

• For factors such as
• Mostly involves

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Sensation Psychophysics

• Definition examines our
• Assesses such things as how much physical energy
  is required
• To test this, researchers present very subtle
  changes in the stimuli and observe how people
  respond.

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Sensation Psychophysics

• Thresholds An important concept in Psychophysics
• Sensory thresholds
• Absolute threshold
• Environment is seldom ideal.
• Noise is an irrelevant and competing stimuli.
• People have

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Absolute Thresholdsfor Different Organ Systems
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Sensation Psychophysics

• Difference Thresholds
• Webers Law

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Sensation Psychophysics

• Sensory adaptation

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SensationThe Basic Sensory Processes

• Gustation (Taste)
• Smell
• Touch
• Hearing
• Vision

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SensationGustation

• Or sense of -----
• Purpose To keep ------------- our digestive
  systems while ---------------.
• The stimuli for taste

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SensationGustation

• Taste buds
• Different people have ------------
• Mostly in the ---------
• Each bud has about
• Short, hair-like structures at the tip of each
  taste bud

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SensationSmell

• Odorous particles in the nose and the nasal
  cavity ?
• Activate
• Send coded messages to the brain center for smell
  (called -----------)?
• Smell signals are sent
• First to the ----------------
• Next to the -----------

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SensationSmell

• Powerful memories and feelings are evoked by
  olfactory stimuli
• Pheromones

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SensationTouch

• The haptic sense
• Sensors in the skin detect
• Haptic receptors

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SensationTouch

• Receptors for pressure
• Some are --------------- at the bases of hair
  follicles that respond to ------------
• Some others are ---------------- in the skin that
  respond to
• The integration of these various signals produces
  haptic experiences.

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SensationTouch

• Receptors for temperature
• Receptors for -----
• Receptors for --------
• The integration of both signals ?

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SensationTouch

• Receptors for pain
• The Purpose of pain
• Nerve fibers conveying pain information are found
  in

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SensationTouch

• Receptors for pain
• Two types of pain are related to two kinds of
  nerve fibers
• Sharp, immediate pain is related to
• Chronic, dull, steady pain is related to
• Fast pain leads to
• Slow pain
• Gate-Control Theory of pain

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SensationHearing

• The stimulus for hearing The displacement of air
  molecules caused by changes in air pressure.
• The ear detects Sound-Waves (i.e., patterns of
  changes in air pressure over time)
• The amplitude of the wave determines its loudness
• Higher amplitude is perceived as louder
• The frequency of a sound wave determines its
  pitch
• Higher frequencies perceived as higher in pitch
• The frequency of sound is measured in vibrations
  per second, called hertz (Hz).

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SensationHearing

• Various regions of ear transduce sound waves into
  brain activity, producing meaningful sounds (see
  figs 5.5 and 5.6 in your textbook)
• outer ear
• Middle ear
• Eardrum
• Ossicles (hammer, anvil, and stirrup)
• oval window cochlea
• basilar membrane

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SensationHearing

• Temporal coding
• A mechanism for encoding low-frequency auditory
  stimuli
• Information is encoded by the frequency of firing
  of the hair cells
• Place coding
• A mechanism for encoding high-frequency auditory
  stimuli
• Information is encoded by the location of the
  hair cells along the basilar membrane.

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SensationVision

• The eye detects light waves
• The light gets focused on the retina (fig 5.7)
• 120 million rods and 6 million cones are retinal
  receptor cells that transduce levels of
  illumination and color (fig 5.8)
• 3 distinct types of cones S, M, L
• Optic nerve consists of axons from ganglion cells
  projected from retina to primary visual cortex
  (fig. 5.10)

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• Perception

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Perception

• The brain translates/interprets the electrical
  impulses, caused by sensory stimuli, to various
  perceptual experiences
• All sensory information (with the exception of
  olfaction) is relayed to the brain via thalamus
• Then thalamus sends the information to primary
  sensory areas

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Primary Sensory Areas
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PerceptionHearing

• Auditory neurons in thalamus extend their axons
  to the primary auditory cortex (A1)
• Neurons in A1
• Code the frequency (or pitch) of auditory stimuli
• Are organized Tonotopicly, neurons at the
• Rear end of A1 respond best to lower frequencies
  (e.g., the sound of a fog horn)
• Front end respond best to higher frequencies
  (e.g., a train whistle)
• Are surrounded by several secondary auditory
  areas in the temporal and parietal lobes

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PerceptionTouch

• Touch neurons in thalamus extend their axons to
  the primary somatosensory cortex (S1) in the
  partial lobe
• Neurons in S1 (fig 4.9)
• Are organized somatotopicly, neighboring body
  parts tend to be represented next to one another

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PerceptionVision

• up to half of the cerebral cortex may participate
  in visual perception
• The primary visual cortex (V1) in the occipital
  lobe
• The neuronal pathway from the retina to the
  occipital lobe preserves spatial relationships,
  so that adjacent areas of the retina correspond
  to adjacent areas in V1
• This is called retinotopic organization
• Early cortical processing does a roughly
  description of various image properties and their
  locations within the scene
• But is still far from identification of the three
  dimensional structure of the visible world
• Hierarchical processing of the details of the
  visual image is done in a number of stages, first
  stage includes extracting visual primitives
  (e.g. lines, angles, colors, curves, motion)

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PerceptionVision

• Some neurons in the primary visual cortex are
  specialized in responding to lines of a
  particular orientation
• E.g. Some neurons fire more in reaction to a
  vertical line segment but fire less in reaction
  to a horizontal line segment
• Some neurons in the primary visual cortex are
  specialized in detecting the ends of lines,
  corners, and colors, as well as more complex
  visual features.

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PerceptionVision

• Two parallel processing streams formed by visual
  areas other than V1 are
• A lower ventral stream
• Involving occipital and temporal lobe regions
• Specialized for processing object perception and
  recognition (e.g., color shape)
• Called what pathway
• A higher dorsal stream
• Involving occipital and parietal lobe regions
• Specialized for processing spatial information
• Called where pathway

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PerceptionVision

• Visual filling-in
• Definition the early visual areas (e.g., V1)
  fill in the constant region information that was
  thrown out at the level of the ganglion cells
• E.g. When the gap falls on your blind spot, your
  brain fills in the portion of the area that it
  assumes is missing because of the blind spot
• Happens automatically
• Is cognitively impenetrable Meaning that it
  can not be changed by your thoughts
• Even though you know that there is a gap out
  there in the world, you cannot help but see a
  continuous line when the image of the gap falls
  on your blind spot
• Shows that the perception has a constructive
  nature

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Object Perception Requires Construction

• Gestalt Principles of Perception
• Perception is more than the result of
  accumulating sensory data
• Proximity and Similarity (fig 5.19)
• The Best forms (see figs 5.20, 5.21, 5.22,
  5.23)
• Figure Ground

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Size Perception Depends on Distance Perception

• Ponzo Illusion (fig 5.37)
• Moon Illusion (fig 5.38)

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Perception Ponzo Illusion
A classic size illusion caused by misleading cues
of depth perception. The two horizontal lines
appear to be different sizes because of the law
of perspective that tells us that parallel
lines converge in the distance. In fact, the two
lines are the same length.
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Perception Moon Illusion
The moon looks larger when it is near the horizon
than when it is overhead, due to various visual
cues.
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Perceptual Constancies

• Definition We correctly perceive objects as
  constant despite sensory data that could lead us
  to think otherwise
• To perceive constancies, we need to understand
  the relationship between at least two factors.
• Size constancy, by knowing how far away the
  object is from us
• Shape constancy, by knowing from what angle were
  seeing the object
• Color constancy, by comparing the wavelengths of
  light reflected from the object with those from
  its background.
• Lightness constancy, by knowing how much light is
  being reflected from the object and from its
  background

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Perceptual Constancies

• Classical theory of Helmholz
• Perceptual experience relies on unconscious
  inferences using automatic Gestalt grouping
  procedures and assumptions
• Built-in-assumptions influence perception, and
  affect how visual illusions are beyond conscious
  control (fig 5.42)

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Attention

• Perception Management
• The brain is constantly receiving input from an
  enormous number of sources.
• The study of attention is the study of how the
  brain selects which sensory stimuli to discard
  and which to pass along to higher levels of
  processing.
• Visual Attention Selective and Serial
• Auditory Attention Selective Listening
• The cocktail party phenomenon refers to how you
  can focus on a single conversation in the midst
  of a chaotic cocktail party, yet a particularly
  pertinent stimulus, such as hearing your name
  mentioned in another conversation, can capture
  your attention

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Selective Attention

• Filter theory we have a limited capacity for
  sensory information and thus screen incoming
  information, only letting in the most important.
  In this model, attention is like a gate that
  opens for important information and closes for
  information to be ignored
• Early Selection theory we can choose which
  stimuli we will attend to even before we process
  their basic features. In visual processing we
  could choose to ignore features such as color or
  form and process only those features that we had
  decided would be important for the task at hand.
  Accordingly, attention effectively filters out
  certain features at an early stage so that they
  never get processed.

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Selective Attention

• Late Selection theory We take in sensory
  information, process it, and then select which
  aspects of the stimuli should be attended. The
  attention stage occurs when the perception enters
  our conscious awareness
• Modern theories of attention suggest that
  selective attention can operate at multiple
  stages of perceptual processing. A variety of
  studies has shown that the processing of attended
  stimuli is enhanced relative to that of
  unattended stimuli, but that unattended stimuli
  are still processed. Some researchers suggest
  that unattended information is not gated
  completely but instead is simply reduced.