Study Area 3 Sensation and Perception

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Study Area 3Sensation and Perception
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Sensation

• Sensation the activation of receptors in the
  various sense organs
• Sensory receptors specialized forms of neurons
  stimulated by different kids of energy rather
  than by neurotransmitters

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Sensation

• Sense organs
• eyes
• ears
• nose
• skin
• taste buds
• Transduction turning outside stimuli into neural
  activity

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Sensory Thresholds

• Absolute threshold the smallest amount of energy
  needed for a person to consciously detect a
  stimulus 50 percent of the time it is present
• The Just noticeable difference (or the difference
  threshold) is the smallest difference between 2
  stimuli that is detectable 50 percent of the
  time.

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Weber's Law Book Definition This concept says
that the size of a JND is proportional to the
intensity of the stimulus. The JND is large when
the stimulus intensity is high and is small when
the stimulus intensity is low. This Means - The
more intense something is, the harder it is to
notice a change, but if the intensity is lower,
it is easier to notice the change. - The
louder or brighter something is, the more change
is needed to notice the difference. - The more
there is of something, the more change is needed
to pass your difference threshold, whereas the
less there is of something, less change is
needed to pass your difference threshold.
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• Weber's Law Book Definition This concept says
  that the size
• of a JND is proportional to the intensity of the
  stimulus. The
• JND is large when the stimulus intensity is high
  and is small
• when the stimulus intensity is low. This Means
• - The more intense the stimulation is, the more
  of a change is
• needed to be able notice the difference.
• Examples
• If the volume of a television is high, turning it
  down by a little bit will not be a very big
  difference.
• When you have a messy room, picking up one or two
  items isn't noticeable, however when you clean
  up 15 items the room will start to look less
  messy.

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Subliminal Sensation

• Subliminal stimuli stimuli that are below the
  level of conscious awareness
• just strong enough to activate the sensory
  receptors, but not strong enough for people to be
  consciously aware of them
• limin threshold
• sublimin below the threshold

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Subliminal Sensation

• Subliminal perception the process by which
  subliminal stimuli act upon the unconscious mind,
  influencing behavior

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Habituation Sensory Adaptation

• Habituation the tendency of the brain to stop
  attending to constant, unchanging information
• Sensory adaptation the tendency of sensory
  receptor cells to become less responsive to a
  stimulus that is unchanging
• Note what differentiates these two.

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Habituation Sensory Adaptation

• Microsaccades constant movement of the eyes
  tiny little vibrations that people do not notice
  consciously
• prevent sensory adaptation to visual stimuli

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Perceptual Properties of Light

• Light the natural agent that stimulates sight
  and makes things visible.
• synonyms illumination, brightness,
  luminescence,
• luminosity, shining, gleaming, gleam,
  brilliance, radiance,
• luster, glowing, glow, blaze, glare, dazzle
• Brightness is determined by the amplitude of the
  wavehow high or how low the wave actually is
• the higher the wave, the brighter the light will
  be
• low waves are dimmer

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Perceptual Properties of Light

• Color, or hue, is determined by the length of the
  wave
• long wavelengths are found at the red end of the
  visible spectrum (the portion of the whole
  spectrum of light that is visible to the human
  eye)
• shorter wavelengths are found at the blue end
• Saturation the purity of the color people see
• mixing in black or gray would lessen the
  saturation

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The Visible SpectrumThe wavelengths that people
can see are only a small part of the whole
electromagnetic spectrum.
From long to short
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Structure of the EyeLight enters the eye through
the cornea and pupil. The iris controls the size
of the pupil. From the pupil, light passes
through the lens to the retina, where it is
transformed into nerve impulses. The nerve
impulses travel to the brain along the optic
nerve.
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Structure of the Eye

• Cornea clear membrane that covers the surface of
  the eye
• protects the eye
• focuses most of the light coming into the eye
• photoreactive keratectomy (PRK) and
  laser-assisted in situ keratomileusis (LASIK)
  vision-improving techniques that make small
  incisions in the cornea to change the focus in
  the eye

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Structure of the Eye

• Aqueous humor visual layer below cornea
• clear, watery fluid that is continually
  replenished
• supplies nourishment to the eye
• Pupil hole through which light from the visual
  image enters the interior of the eye

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Structure of the Eye

• Iris round muscle (the colored part of the eye)
  in which the pupil is located
• can change the size of the pupil, letting more or
  less light into the eye
• helps focus the image
• Lens another clear structure behind the iris,
  suspended by muscles
• finishes the focusing process begun by the cornea

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Structure of the Eye

• Visual accommodation the change in the thickness
  of the lens as the eye focuses on objects that
  are far away or close
• Vitreous humor jelly-like fluid that also
  nourishes the eye and gives it shape

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Structure of the Eye

• Nearsightedness, or myopia
• the shape of the eye causes the focal point to
  fall short of the retina
• Farsightedness, or hyperopia
• the focus point is behind the retina

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Nearsightedness and Farsightedness
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Retina, Rods, and Cones

• Retina final stop for light in the eye
• contains three layers
• ganglion cells (2) bipolar cells
• (3) photoreceptors that respond to various light
  waves

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Retina, Rods, and Cones

• Rods visual sensory receptors found at the back
  of the retina
• responsible for noncolor sensitivity to low
  levels of light
• Cones visual sensory receptors found at the back
  of the retina
• responsible for color vision and sharpness of
  vision

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Retina, Rods, and Cones

• Blind spot area in the retina where the axons of
  the three layers of retinal cells exit the eye to
  form the optic nerve insensitive to light

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• The Parts of the Retina
• light passes through ganglion and bipolar cells
  until it reaches and stimulates the rods and
  cones. nerve impulses from the rods and cones
  travel along a nerve pathway to the brain.
• On the right of the figure is a photomicrograph
  of the long, thin rods and the shorter, thicker
  cones the rods outnumber the cones by a ratio of
  about 20 to 1.
• The blind spot demonstration. Hold the book in
  front of you. Close your right eye and stare at
  the picture of the dog with your left eye. Slowly
  bring the book closer to your face. The picture
  of the cat will disappear at some point because
  the light from the picture of the cat is falling
  on your blind spot. If you cannot seem to find
  your blind spot, trying moving the book more
  slowly.

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Crossing of the Optic Nerve Light falling on the
left side of each eyes retina (from the right
visual field, shown in yellow) will stimulate a
neural message that will travel along the optic
nerve to the thalamus, and then on to the visual
cortex in the occipital lobe of the left
hemisphere. Notice that the message from the
temporal half of the left retina goes to the left
occipital lobe, while the message from the nasal
half of the right retina crosses over to the left
hemisphere (the optic chiasm is the point of
crossover). The optic nerve tissue from both eyes
joins together to form the left optic tract
before going on to the thalamus and the left
occipital lobe. For the left visual field (shown
in blue), the messages from both right sides of
the retinas will travel along the right optic
tract to the right visual cortex in the same
manner.
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How the Eye Works

• Dark adaptation the recovery of the eyes
  sensitivity to visual stimuli in darkness after
  exposure to bright lights
• night blindness
• Light adaptation the recovery of the eyes
  sensitivity to visual stimuli in light after
  exposure to darkness

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Color Vision

• Trichromatic theory theory of color vision that
  proposes three types of cones red, blue, and
  green

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Color Vision

• Opponent-process theory theory of color vision
  that proposes four primary colors with cones
  arranged in pairs red and green, blue and yellow
• afterimages images that occur when a visual
  sensation persists for a brief time even after
  the original stimulus is removed
• lateral geniculate nucleus (LGN) of thalamus

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Figure 3.6 Color Afterimage Stare at the white
dot in the center of this oddly colored flag for
about 30 seconds. Now look at a white piece of
paper or a white wall. Notice that the colors are
now the normal, expected colors of the American
flag. They are also the primary colors that are
opposites of the colors in the picture and
provide evidence for the opponent-process theory
of color vision.
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Color Blindness

• Monochrome colorblindness a condition in which a
  persons eyes either have no cones or have cones
  that are not working at all
• Red-green colorblindness either the red or the
  green cones are not working
• Sex-linked inheritance
• gene for color-deficient vision is recessive

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The Ishihara Color Test
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Sound
Video

• Wavelength interpreted as frequency or pitch
  (high, medium, or low)
• Purity interpreted as timbre (a richness in the
  tone of the sound)
• Amplitude interpreted as volume (how soft or
  loud a sound is)
• Hertz (Hz) cycles or waves per second, a
  measurement of frequency

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Sound Waves Two sound waves. The higher the wave,
the louder the sound the lower the wave, the
softer the sound. If the waves are close together
in time (high frequency), the pitch will be
perceived as a high pitch. Waves that are farther
apart (low frequency) will be perceived as having
a lower pitch.
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Structure of the Ear
LO 3.4 What Is Sound?

• Auditory canal short tunnel that runs from the
  pinna to the eardrum (tympanic membrane)

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Structure of the Ear

• Eardrum thin section of skin that tightly covers
  the opening into the middle part of the ear
• when sound waves hit the eardrum, it vibrates and
  causes three tiny bones (Ossicles) in the middle
  ear to vibrate
• Hammer - Malleus
• Anvil - Incus
• Stirrup- Stapes

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Structure of the Ear

• Cochlea snail-shaped structure of the inner ear
  that is filled with fluid
• Organ of Corti rests in the basilar membrane
• contains receptor cells for sense of hearing
• Auditory nerve bundle of axons from the hair
  cells in the inner ear
• receives neural message from the organ of Corti

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The Structure of the Ear
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Theories of Pitch

• Pitch psychological experience of sound that
  corresponds to the frequency of the sound waves
• higher frequencies are perceived as higher
  pitches
• Place theory theory of pitch that states that
  different pitches are experienced by the
  stimulation of hair cells in different locations
  on the organ of Corti

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Theories of Pitch

• Frequency theory theory of pitch that states
  that pitch is related to the speed of vibrations
  in the basilar membrane
• Volley principle theory of pitch that states
  that frequencies from about 400 Hz up to about
  4000 Hz cause the hair cells (auditory neurons)
  to fire in a volley pattern, or take turns in
  firing

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Types of Hearing Impairments

• Conduction hearing impairment can result from
• damaged eardrum would prevent sound waves from
  being carried into the middle ear properly
• damage to the bones of the middle ear sounds
  cannot be conducted from the eardrum to the
  cochlea

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Types of Hearing Impairments

• Nerve hearing impairment can result from
• damage in the inner ear
• damage in the auditory pathways and cortical
  areas of the brain

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Surgery to Help Restore Hearing

• Cochlear implant a microphone implanted just
  behind the ear that picks up sound from the
  surrounding environment
• speech processor selects and arranges the sound
  picked up by the microphone
• implant is a transmitter and receiver, converting
  signals into electrical impulses
• Collected by the electrode array in the cochlea
  and then sent to the brain

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Cochlear Implant
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Taste

• Taste buds
• taste receptor cells in mouth responsible for
  sense of taste
• Gustation the sensation of a taste
• Five basic tastes
• Sweet - Sour Salty Bitter - brothy, or
  Umami

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(a) Nerves in the tongues deep tissue (b) Taste
buds location inside the papillae (c)
Microphotograph of the surface of the tongue
showing two different sizes of papillae
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Smell

• Olfaction (olfactory sense)
• sense of smell
• Olfactory bulbs
• areas of the brain located just above the sinus
  cavity and just below the frontal lobes that
  receive information from the olfactory receptor
  cells
• At least 1,000 olfactory receptors

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The Olfactory Receptors
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Somesthetic Senses

• Somesthetic senses the body senses consisting of
  the skin senses, the kinesthetic sense, and the
  vestibular senses
• soma body
• esthetic feeling

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Somesthetic Senses

• Skin senses the sensations of touch, pressure,
  temperature, and pain
• sensory receptors in the skin
• gate-control theory pain signals must pass
  through a gate located in the spinal cord

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Cross Section of the Skin and Its Receptors
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Somesthetic Senses

• Kinesthetic sense sense of the location of body
  parts in relation to the ground and each other
• proprioceptive receptors (proprioceptors)
• Proprioception is the sense of the relative
  position of neighboring parts of the body and
  strength of effort being employed in movement.

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Somesthetic Senses

• Sensory conflict theory an explanation of motion
  sickness in which the information from the eyes
  conflicts with the information from the
  vestibular senses
• results in dizziness, nausea, and other physical
  discomforts

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Somesthetic Senses

• The Vestibular Senses Awareness of body balance
  and movement are monitored by the vestibular
  system. The vestibular senses (the sensations of
  body rotation and of gravitation and movement)
  arise in the inner ear the sense organs are the
  hair cells that send out signals over the
  auditory nerve.

The vestibular system includes the semicircular
canals (brown) that transduce the rotational
movements of the body and the vestibular sacs
(blue) that sense linear accelerations.
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Sensation

• Sensation refers to the process of sensing our
  environment through touch, taste, sight, sound,
  and smell. This information is sent to our brains
  in raw form where perception comes into play.
• Perception is the way we interpret these
  sensations and therefore make sense of everything
  around us.

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Perception and Constancies

• Perception
• the method by which the sensations experienced at
  any given moment are interpreted and organized in
  some meaningful fashion
• Size constancy
• the tendency to interpret an object as always
  being the same actual size, regardless of its
  distance

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Perception and Constancies

• Shape constancy
• the tendency to interpret the shape of an object
  as being constant, even when its shape changes on
  the retina
• Brightness constancy
• the tendency to perceive the apparent brightness
  of an object as the same even when the light
  conditions change

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Shape Constancy
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Gestalt Principles

• Gestalt principles, or gestalt laws, are rules of
  the organization of perceptual scenes.
• Figureground
• the tendency to perceive objects, or figures, as
  existing on a background
• Reversible figures
• visual illusions in which the figure and ground
  can be reversed

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The Necker Cube is an optical illusion that
consists of a two dimensional representation of a
three dimensional wire frame cube.
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Figure-Ground Illusion
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Gestalt Principles

• Proximity
• tendency to perceive objects that are close to
  each other as part of the same grouping
• Similarity
• tendency to perceive things that look similar to
  each other as being part of the same group

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Gestalt Principles

• Closure
• tendency to complete figures that are incomplete
• Continuity
• tendency to perceive things as simply as possible
  with a continuous pattern rather than with a
  complex, broken-up pattern

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Gestalt Principles

• Contiguity
• tendency to perceive two things that happen close
  together in time as being related

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Gestalt Principles of Grouping
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Development of Perception

• Depth perception the ability to perceive the
  world in three dimensions and the distance of an
  object.

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Monocular Cues

• Monocular cues (pictorial depth cues) cues for
  perceiving depth based on one eye only
• linear perspective the tendency for parallel
  lines to appear to converge on each other
• relative size perception that occurs when
  objects that a person expects to be of a certain
  size appear to be small and are, therefore,
  assumed to be much farther away

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Monocular Cues

• Monocular Cues (contd)
• overlap the assumption that an object that
  appears to be blocking part of another object is
  in front of the second object and closer to the
  viewer a.k.a. interposition
• aerial (atmospheric) perspective the haziness
  that surrounds objects that are farther away from
  the viewer, causing the distance to be perceived
  as greater
• texture gradient the tendency for textured
  surfaces to appear to become smaller and finer as
  distance from the viewer increases

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Monocular Cues

• Monocular Cues (contd)
• motion parallax the perception of motion of
  objects in which close objects appear to move
  more quickly than objects that are farther away
• accommodation as a monocular clue, the brains
  use of information about the changing thickness
  of the lens of the eye in response to looking at
  objects that are close or far away

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Examples of monocular Depth Cues (a) Linear
perspective, (b) texture gradient, (c) aerial or
atmospheric perspective, (d) relative size
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Binocular Cues

• Binocular cues cues for perceiving depth based
  on both eyes
• convergence the rotation of the two eyes in
  their sockets to focus on a single object,
  resulting in greater convergence for closer
  objects and lesser convergence if objects are
  distant

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Binocular Cues

• retinal disparity the difference in images
  between the two eyes, which is greater for
  objects that are close and smaller for distant
  objects

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Binocular Cues to Depth Perception
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Perceptual Illusions

• Hermann grid is possibly due to the response of
  the primary visual cortex
• Müller-Lyer illusion illusion of line length
  that is distorted by inward-turning or
  outward-turning corners on the ends of the lines,
  causing lines of equal length to appear to be
  different

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The Hermann grid illusion is characterized by
"ghostlike" grey blobs perceived at the
intersections of a white (or light-colored) grid o
n a black background. The grey blobs disappear
when looking directly at an intersection.
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The Muller-lyer illusion
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Perceptual Illusions

• Moon illusion the moon on the horizon appears to
  be larger than the moon in the sky
• apparent distance hypothesis

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Perceptual Illusions

• Illusions of motion
• autokinetic effect a small, stationary light in
  a darkened room will appear to move or drift
  because there are no surrounding cues to indicate
  that the light is not moving
• stroboscopic motion seen in motion pictures, in
  which a rapid series of still pictures will
  appear to be in motion

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Perceptual Illusions

• Illusions of motion
• phi phenomenon lights turned on in a sequence
  appear to move
• rotating snakes due in part to eye movements
• The Enigma due in part to microsaccades
• Microsaccades are a kind of fixational eye
  movement. They are small, jerk-like, involuntary
  eye movements

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Phi
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Rotating Snakes
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Reinterpretation of Enigma
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Perceptual Illusions

• Ames Room Illusion

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Factors that Influence Perception

• Perceptual set (perceptual expectancy) the
  tendency to perceive things a certain way because
  previous experiences or expectations influence
  those perceptions
• Top-down processing the use of preexisting
  knowledge to organize individual features into a
  unified whole.
• Deductive reasoning works from the more
  general to the more
• specific. Sometimes this is informally called
  a "top-down" approach.

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Perceptual Set Look at the drawing. What do you
see? Then look at the two pictures on the next
slide.
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Perceptual Set (Contd) Would you have
interpreted the first drawing differently if you
had viewed these images first?
Young woman
Old woman
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Factors that Influence Perception

• Bottom-up processing the analysis of the smaller
  features to build up to a complete perception
• According to Theoretical Synthesis, "when a
  stimulus is presented short and clarity is
  uncertain that gives a vague stimulus, perception
  becomes a top-down approach." Conversely,
  Psychology defines bottom-up processing as an
  approach wherein there is a progression from the
  individual elements to the whole.

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The Devils Trident
This figure confuses many Western observers. The
confusion arises from trying to interpret it as
a three-dimensional figure. Deregowski (1969)
found that people who habitually ascribed
three-dimensionality to pictures had more
difficulty in reproducing this figure than people
who did not seek to impose three-dimensionality
on images.
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Perception
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The End Study Area 3Sensation and Perception