Chapter 3 Sensation and Perception

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Chapter 3Sensation and Perception
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Chapter 3 Overview

• The process of sensation
• Vision
• Hearing
• Smell and taste
• The skin senses
• Balance and movement
• Influences on perception
• Principles of perception
• Unusual perceptual experiences

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The Process of Sensation

• Sensation is the process through which the senses
  pick up visual, auditory, and other sensory
  stimuli and transmit them to the brain
• Perception is the process by which the brain
  actively organizes and interprets sensory
  information

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What is the difference between the absolute
threshold and the difference threshold?

• What is the softest sound you can hear and the
  dimmest light you can see?
• How much must the volume be turned up or down for
  you to notice a difference in the loudness of
  music?
• Researchers in sensory psychology have performed
  many experiments to answer these kinds of
  questions

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Absolute threshold

• The minimum amount of sensory stimulation that
  can be detected 50 of the time

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Difference threshold

• The smallest increase or decrease in a physical
  stimulus required to produce a difference in
  sensation that is noticeable 50 of the time
• Just noticeable difference (JND) is the smallest
  change in sensation that a person is able to
  detect 50 of the time

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Webers Law

• The JND for all senses depends on a proportion or
  percentage of stimulus change rather than on a
  fixed amount of change
• A 2 change is needed for a JND in a weight you
  are holding
• a 1 lb difference is needed for a JND in a 50 lb
  weight
• a 2 lb difference is needed for a JND in a 100 lb
  weight
• Only a 0.33 change is needed for a JND in the
  pitch of a sound
• Webers law best applies to people with average
  sensitivities and to stimuli that are not too
  strong or weak

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How does transduction enable the brain to receive
sensory information?

• Sensory receptors are highly specialized cells in
  the sense organs that detect and respond to one
  type of sensory stimuli and transduce (convert)
  the stimuli into neural impulses
• Transduction is the process through which sensory
  receptors convert sensory stimulation into neural
  impulses
• Sensory adaptation is the process in which
  sensory receptors grow accustomed to constant,
  unchanging levels of stimuli over time
• e.g., Smokers grow accustomed to smell of
  cigarettes

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Vision

• Our eyes respond to light in the visible spectrum
• The band of electromagnetic waves visible to the
  human eye
• Electromagnetic waves are measured in wavelengths
• The distance from the peak of a light wave to the
  peak of the next wave

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How does each part of the eye function in vision?

• Cornea
• Tough, transparent protective layer that covers
  front of eye
• Bends light rays inward through the pupil
• Lens
• Transparent disk-shaped structure behind the iris
  and pupil
• Changes shape as it focuses on objects at varying
  distances
• This process is called Accommodation

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How does each part of the eye function in vision?

• Retina
• Contains sensory receptors for vision
• Rods
• Receptor cells that allow eye to respond to low
  levels of light
• Cones
• Receptor cells that enable us to see color and
  fine detail
• Fovea
• Area at center of retina that provides the
  clearest and sharpest vision
• Blind spot
• Point in each retina where there are no rods or
  cones

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What path does visual information take from the
retina to the primary visual cortex?

• Optic nerve
• Caries visual information from each retina to
  both sides of the brain
• Primary visual cortex
• Part of the brain in which visual information is
  processed
• Feature detectors respond to specific visual
  patterns, such as lines or angles

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How do we detect the difference between one color
and another?

• An apples skin looks red because it absorbs
  short wavelengths and reflects long wavelengths
• Hue
• The specific color perceived
• Saturation
• The purity of a color
• Brightness
• The intensity of the light energy that is
  perceived as a color

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What two major theories attempt to explain color
vision?

• Trichromatic Theory
• Three types of cones in the retina each make a
  maximal response to one of three colors- blue,
  green, or red
• Opponent-Process Theory
• Three kinds of cells respond by increasing or
  decreasing their rate of firing when different
  colors are present
• Red/green cells
• Yellow/blue cells
• White/black cells

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A negative afterimage
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Hearing

• Sound requires a medium, such as air or water,
  through which to move
• First demonstrated by Robert Boyle in 1660
• Watch in a jar experiment

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What determines the pitch and loudness of sound,
and how is each quality measured?

• Frequency
• The number of cycles completed by a sound wave in
  one second
• Determines the pitch of a sound
• Frequency is measured in hertz (Hz)
• Amplitude
• The loudness of sound
• Amplitude is measured in decibels (dB)
• Timbre
• The distinctive quality of a sound that
  distinguishes it from other sounds of the same
  pitch and loudness
• Example A piano and guitar sound different when
  playing the same note

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Decibel levels of various sounds
Figure 3.5 The loudness of a sound (its
amplitude) is measured in decibels. Each increase
of 10 decibels makes a sound 10 times louder. A
normal conversation at 3 feet measures about 60
decibels, which is 10,000 times louder than a
soft whisper of 20 decibels. Any exposure to
sounds of 130 decibels or higher puts a person at
immediate risk for hearing damage, but levels as
low as 90 decibels can cause hearing loss if one
is exposed to them over long periods of time.
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How do the outer ear, middle ear, and inner ear
function in hearing?

• Outer ear
• Visible part of the ear, consisting of the pinna
  and auditory canal
• Middle ear
• Contains the ossicles, which connect the ear drum
  to the oval window and amplify sound waves
• Inner ear
• Cochlea Fluid filled chamber that contains the
  basilar membrane and hair cells
• Hair cells Sensory receptors for hearing

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What two major theories attempt to explain
hearing?

• Place theory
• Each individual pitch is determined by the
  particular location along the basilar membrane of
  the cochlea that vibrates the most
• Provides a good explanation of how we hear sounds
  with frequencies higher than 1000 Hz
• Frequency theory
• Hair cell receptors vibrate the same number of
  times per second as the wave sounds that reach
  them
• Provides a good explanation of how we hear
  low-frequency sounds

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Smell and Taste

• Olfaction
• The sense of smell
• Gustation
• The sense of taste

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What path does a smell message take from the nose
to the brain?

• Olfactory epithelium
• Two 1-inch square patches of tissue, one at the
  top of each nasal cavity, which contain olfactory
  neurons
• Olfactory bulbs
• Two structures above the nasal cavity where smell
  sensations first register in the brain
• Orbitofrontal cortex
• Receives messages from olfactory bulbs via the
  thalamus

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What are the primary taste sensations, and how
are they detected?

• Traditionally, four primary taste sensations have
  been recognized
• Sweet
• Sour
• Salty
• Bitter
• Recent research suggests that there is a fifth
  taste sensation
• Umami
• This sensation is triggered by glutamate

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What are the primary taste sensations, and how
are they detected?

• Taste sensations are detected by receptor cells
  in the taste buds
• Specialized receptors are activated by each
  flavor (sweet, sour, etc.)
• These receptors send separate messages to the
  brain

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The Skin Senses

• Include the senses of touch and pain
• These senses are critical for survival

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How does the skin provide sensory information?

• When an object touches and depresses the skin it
  stimulates receptors in the skin
• These receptors send messages through nerve
  connections to the spinal cord, through the
  brainstem and midbrain, and to the somatosensory
  cortex
• Areas on the skin vary in sensitivity to touch,
  as measured by the two-point threshold
• Areas with greater sensitivity are more densely
  packed with touch receptors

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What is the function of pain, and how is pain
influenced by psychological factors, culture, and
endorphins?

• Pain serves as an early warning system for many
  potentially deadly situations
• Pain can be influenced by several psychological
  factors
• Focusing attention elsewhere reduces pain
• Placebo effect reduces pain
• Negative thoughts increase pain
• Some cultures encourage individuals to suppress,
  or exaggerate, emotional reaction to pain
• Endorphins are the bodys natural painkillers
• They block pain and produce a sense of well-being

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Balance and Movement

• The kinesthetic and vestibular senses provide
  information about where the parts of the body are
  and where the body is located relative to the
  physical environment

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What kinds of information do the kinesthetic and
vestibular senses provide?

• The kinesthetic sense provides information about
  the position of body parts in relation to each
  other and the movement of the entire body or its
  parts
• This information is detected by receptors in the
  joints, ligaments, and muscles

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What kinds of information do the kinesthetic and
vestibular senses provide?

• The vestibular sense detects movement and the
  bodys orientation in space
• The vestibular sense organs are located in the
  semicircular canals and vestibular sacs in the
  inner ear
• These organs sense rotation of the head

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Influences on Perception

• Perception is the process through which the brain
  assigns meaning to sensations
• Perception is influenced by a number of factors,
  including
• Attention
• Prior knowledge
• Cross-modal perception

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What is gained and what is lost in the process of
attention?

• Attention is the process of sorting through
  sensations and selecting some of them for further
  processing
• When attention is focused on some sensations,
  others are missed altogether or misperceived
• Inattentional blindness occurs when attention is
  shifted from one object to another and we fail to
  notice changes in objects not receiving direct
  attention
• The cocktail party phenomenon shows that we focus
  attention on information that is personally
  meaningful

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How does prior knowledge influence perception?

• Bottom-up processing
• Information processing in which individual bits
  of data are combined until a complete perception
  is formed
• Top-down processing
• Information processing in which previous
  experience and knowledge are applied to recognize
  the whole of a perception
• Perceptual set is an expectation of what will be
  perceived that can affect what is perceived

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How does information from multiple sources aid
perception?

• Cross modal perception
• The process by which the brain integrates
  information from more than one sense
• Cross modal perception is used to process complex
  stimuli such as speech

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Principles of Perception

• A few principles govern perceptions in all humans

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What are the principles that govern perceptual
organization?

• Gestalt principles of perceptual organization
• Similarity Objects that have similar
  characteristics are perceived as a unit
• Proximity Objects that are close together are
  perceived as belonging together
• Continuity Figures or objects are perceived as
  belonging together if they appear to form a
  continuous pattern
• Closure Figures with gaps in them are perceived
  as complete

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What are some of the binocular and monocular
depth cues?

• Depth perception
• The ability to perceive the visual world in three
  dimensions and to judge distances accurately
• Binocular depth cues depend on both eyes working
  together
• Convergence
• Binocular disparity
• Monocular depth cues can be perceived by one eye
  alone

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Binocular disparity

• Enables most of us to see 3-D images in
  stereograms

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Monocular depth cues
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How does the brain perceive motion?

• The brain perceives real motion by comparing the
  movement of images across the retina to reference
  points that it assumes to be stable
• Autokinetic illusion
• An unmoving light in a dark room appears to move
• Your eyes are moving, not the light
• In the dark, the brain has no stable reference
  point to determine what is moving

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What are three types of puzzling perceptions?

• Ambiguous figures
• The perceptual system tries to resolve the
  uncertainty by seeing the figure first one way
  and then another
• Impossible figures
• May not seem unusual until you examine them
  closely and see the impossibility

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What are three types of puzzling perceptions?

• Illusions
• False perceptions or misperceptions of an actual
  stimulus in the environment
• Figure c shows the Müller-Lyer illusion
• Figure d shows the Ponzo illusion

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Unusual Perceptual Experiences

• Subliminal perception
• The capacity to perceive and respond to stimuli
  that are presented below the threshold of
  awareness
• Extrasensory perception (ESP)
• Gaining information about objects, events, or
  another persons thoughts through means other
  than known sensory channels

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In what ways does subliminal perception influence
behavior?

• Research suggests that subliminal information can
  influence behavior to some degree
• But it appears to be ineffective at persuading
  people to buy products or vote in certain ways

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What have studies of ESP shown?

• Some studies have suggested that ESP exists
• But, in almost all cases, attempts to replicate
  these studies have failed
• So most psychologists remain skeptical about
  existence of ESP