Chapter 4 Sensation * * The sense of taste became a near

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Chapter 4Sensation
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Basic Principles of Sensation

• Sensation is the process that detects stimulation
  from our bodies and our environment.

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Basic Principles of Sensation

• Perception is the process that organizes those
  stimuli into meaningful objects and events and
  interprets them.

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Basic Principles of Sensation

• Psychophysics is the study of how physical
  stimuli are translated into psychological
  experience.

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Sensory Information Must Be Converted into Neural
Impulses

• Sound, light, etc. cannot travel through our
  nerves to the brain.
• Sensory organs convert their physical properties
  into neural impulses.
• This conversion process is called transduction.

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Sensory Information Must Be Converted into Neural
Impulses

• Transduction takes place at sensory receptors.
• Next, connecting neurons in the sense organs send
  this information to the brain.
• The brain processes these neural impulses into
  what we experience.
• Some stimuli are just as real as those that we
  can transduce, but they are not a part of our
  sensory experience.

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Our Senses Vary in Their Sensitivity Thresholds

• Absolute threshold the lowest level of intensity
  of a given stimulus that a person can detect half
  the time
• As people age, their absolute thresholds for all
  senses increase.

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Our Senses Vary in Their Sensitivity Thresholds

• Signal-detection theory contends that detection
  of a stimulus is influenced by observers
  expectations.
• How likely is the stimulus to occur?
• How important or rewarding is detecting it?
• So absolute threshold may vary.
• It is usually defined as the intensity of a
  stimulus that can be detected 50 of the time.

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Sensation--Thresholds

• When stimuli are detectable less than 50 of the
  time (below ones absolute threshold) they are
  subliminal

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Our Senses Vary in Their Sensitivity Thresholds

• Difference threshold is the smallest difference
  between two stimuli that is detected half (50)
  of the time.
• It is also called the just-noticeable
  difference or jnd.

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Our Sensory Receptors Adapt to Unchanging Stimuli

• Sensory adaptation the tendency for our sensory
  receptors to have decreasing responsiveness to
  stimuli that continue without change.
• Auditory adaptation occurs much more slowly than
  adaptation to odors, tastes, and skin sensations.

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Sensory Adaptation
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We See Only a Narrow Band of Electromagnetic
Radiation

• Wavelengths of visible light range from 400 to
  750 nanometers.
• Shorter wavelengths are experienced as violet.
• Intermediate ones as blue, green, and yellow.
• Longer ones as red.
• Other forms of electromagnetic energy that our
  eyes cannot detect are
• Radio
• Infrared
• Ultraviolet
• X-ray radiation

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Vision Spectrum of Electromagnetic Energy
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Physical Properties of Waves
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Color and Wavelength of Light

• An object appears as a particular color because
  it absorbs certain wavelengths of light and
  reflects others.
• These wavelengths are simply energy colors are
  created by our nervous system in response to
  them.
• Species differ in what they see when looking at
  the same object.
• Our difference threshold for colors is so low
  that the average person can discriminate about 2
  million different colors.

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Color Constancy

• The relative constancy of perceived color under
  different conditions of illumination.

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Major Structures of the Human Eye
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Retinas Reaction to Light
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Photoreceptors in the Retina

• Rods (125 million)
• Located at the edges of the retina.
• Are not involved in color vision.
• Function best under low-light conditions.
• Cones (7 million)
• Located near the center of the retina (the
  fovea).
• Require bright light to be activated.
• Play a key role in color vision.

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Vision--Receptors
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Sound Is the Stimulus for Hearing

• Soundwaves (pressure) are created when an object
  vibrates.
• Wave speed or frequency corresponds to pitch.
• Amplitude (wave height) corresponds to loudness
  of a sound.
• Most sounds are a combination of many different
  waves of different frequencies.
• This sound complexity is caled timbre.

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Auditory System Three major parts of the Ear

• Outer ear
• The pinna is the most visible part of the outer
  ear.
• The auditory canal is funnel shaped.
• The eardrum is at the end of the auditory canal
  and it vibrates in sequence with sound waves.

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Audition- The Ear
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Auditory System Three major parts of the Ear

• Middle ear
• The ossicles are three tiny interconnected
  bonesthe hammer, anvil, and stirrup that move
  and amplify sound waves before sending them to
  the inner ear.

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Auditory System Three major parts of the Ear

• Inner Ear
• innermost part of ear, containing the cochlea,
  semicircular canals and vestibular sacs
• Cochlea
• coiled, bony, fluid-filled tube in the inner ear
  through which sound waves trigger nerve impulses

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Sound Localization

• Sound localization the ability to locate objects
  in space solely on the basis of the sounds they
  make
• Because the ears are only 6 inches apart, the
  time lag between the sound reaching both ears is
  very short.
• Even such small time lags provide the auditory
  system with sufficient information to locate the
  sound.

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Sound Localization
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Pitch Perception Place Theory

• Place theory contends that we hear different
  pitches because different sound waves trigger
  hair cells on different places of the cochleas
  basilar membrane.

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Pitch Perception Frequency Theory

• Frequency theory contends that pitch is
  determined by the frequency with which the
  basilar membrane vibrates.

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Pitch Perception

• Place theory best explains high-frequency sounds,
  while frequency theory best explains
  low-frequency sounds. Mid-frequency sounds are
  best explained by volley theory, a revision of
  frequency theory.

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The Intensity of Some Common Sounds
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Smell and Taste The Chemical Senses

• Olfaction the sense of smell
• The stimuli are airborne molecules
• Olfactory receptor cells are at the top of the
  nasal cavity.
• These cells transmit information to the olfactory
  bulb at the base of the brain.
• The olfactory bulb processes this information and
  sends it to the primary olfactory cortex.

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Smell
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Olfaction

• Olfactory sensitivity is determined by the number
  of receptors in the epithelium.
• Odors can evoke memories and feelings associated
  with past events.

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Smell and Taste The Chemical Senses

• Gustation the sense of taste
• Gustation occurs when a substance makes contact
  with special receptor cells in the mouth, called
  taste buds.
• Most taste buds are located on the tongue, but
  some are in the throat and on the roof of the
  mouth.

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Gustation the sense of taste

• When taste cells absorb chemicals dissolved in
  saliva, they trigger neural impulses, transmitted
  to one of two brain areas
• First information first sent to the thalamus and
  then to the primary gustatory cortex, where taste
  identification occurs
• Second information sent to the limbic system,
  which allows a quick response to a taste prior to
  conscious identification of it (example, spitting
  out sour milk)

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The Five Primary Tastes
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The Skin Senses Pressure, Temperature, Pain

• Our skin is our largest sensory organ.
• Sense of touch is actually a combination of three
  skin senses
• Pressure physical pressure on the skin
• Temperature The skin contains two kinds of
  temperature receptors, one sensitive to warm and
  the other to cold.

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Pain The Bodys Warning System

• Pain is induced through tissue damage or intense
  stimulation of sensory receptors.
• Gate-control theory proposes that small-diameter
  nerve fibers (S-fibers) and large-diameter nerve
  fibers (L-fibers) open and close gateways for
  pain in the spinal cord.
• Pain gateways can be closedthus preventing pain
  messages from reaching the brainby a class of
  substances known as endorphins.

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The Proprioceptive Senses Body Movement and
Location

• Kinesthetic sense provides information about the
  movement and location of body parts with respect
  to one another
• This information comes from proprioceptors
  (receptors in muscles, joints, and ligaments.)
• Vestibular sense provides information on the
  position of the body in space by sensing gravity
  and motion (inner ear).