Sensation and Perception

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Sensation and Perception

• Chapter 3

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What is sensation ?

• Your senses are the gateway through which your
  brain receives all information about its
  environment
• A natural and automatic process
• Often taken for granted until it is interrupted
  by injury or illness
• People with one nonfunctional sense are amazingly
  adaptive

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Overlapping Processes Sensation and Perception

• Sensation the detection and sensing of
  environmental stimuli (sounds, objects, odors)
• Perception occurs when we integrate, organize,
  and interpret sensory information in a meaningful
  way
• No clear boundary line between the two processes-
  psychology often regards the two processes as a
  single process

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Sensation

• All sensation is the result of stimulation of
  specialized cells, called sensory receptors, by
  some form of energy.
• The forms of energy most commonly in contact
  with light, sound, heat, pressure, chemical
  energy
• Sensory receptors convert forms of energy into
  electric impulses that are transmitted via
  neurons to the brain.

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The Senses

• Humans have five basic senses, each receptive to
  a different form of energy
• SIGHT receives light energy
• HEARING receives sound energy or sound waves
• TOUCH receives mechanical energy
• SMELL receives airborne chemical energy
• TASTE receives chemical energy

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Specialization

• We are constantly bombarded by many different
  forms of energy.
• Sensory receptors are highly specialized and
  sensitive to specific types of energy
• For any type of stimulation to be sensed, the
  stimulus energy must first be in the form to be
  detected by our receptor cells

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Sensory Thresholds

• Our senses are specialized in other ways- we do
  not have an infinite capacity to detect all
  levels of energy
• To be sensed a stimulus must first be strong
  enough to be detected- loud enough to be heard,
  concentrated enough to be smelled, bright enough
  to be seen
• The point where the stimulus is strong enough to
  be detected by activating a sensory receptor cell
  is called threshold.

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Absolute Threshold

• The minimum amount of energy in the environment
  that a sensory system can detect (half the time
  in trials and research)

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Galanters (1962) Absolute Thresholds

• Sense Absolute Threshold
• Vision A candle flame seen from 30 miles away
  on a clear, dark night
• Hearing The tick of a watch at 20 feet
• Taste 1 teaspoon of sugar in 2 gallons of
  water
• Smell 1 drop of perfume through-out a 3-room
  apartment
• Touch A bees wing falling on your cheek from
  a height of about ½ inch

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Difference Threshold

• The smallest possible difference between two
  stimuli that can be detected half the time
• Also called just noticeable difference (jnd)
• The difference threshold will vary it is not a
  constant , even for a specific sensory system

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Webers Law

• A principle of sensation
• For each sense, the size of the just noticeable
  difference (difference threshold) is a constant
  proportion of the size of the initial stimulus
• Whether we can detect a change in the strength of
  the stimulus depends on the intensity of the
  original stimulus

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Sensory Adaptation

• A gradual decline in sensitivity to a constant
  stimulus

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Subliminal Perception

• Refers to the perception of stimuli that are
  below the threshold of conscious perception or
  awareness
• Can subliminal messages in advertising and
  self-help tapes change peoples behavior?
• Psychologists have found that the effects of
  subliminal stimuli tend to be weak or
  short-lived, usually lasting only seconds or
  minutes.

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Vision

• The sense organ for vision is the eye, which
  contains receptor cells that are sensitive to the
  physical energy of light.
• The most important sense to humans
• Light is one of many different kinds of magnetic
  energy that travels in the form of waves
• Other forms of electromagnetic energy include
  X-rays, the microwave oven, and ultraviolet light
  (sunburn)

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Eye Structure Anatomy and Functions

• See an object- light waves reflected from the
  object enter your eye and pass through the
  cornea, pupil, and lense.

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Cornea

• A clear membrane that covers the front of the
  eye, helps gather and direct incoming light

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Pupil

• Black opening in the middle of the eye

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Iris

• Surrounds the pupil, the colored structure that
  we refer to when we say someone has brown or blue
  eyes
• Consists of a ring of muscles that contracts or
  expands to precisely control the size of the
  pupil and the amount of light entering the eye

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Lens

• Behind the pupil is the lens, a transparent
  structure held in place by ciliary muscles
• The lens thickens and thins to bend or focus
  incoming light (accommodation)
• Abnormally shaped eyeballs cause improper focus
  of incoming light on the retina
• This results in a visual disorder-
  nearsightedness, farsightedness, or astigmatism

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Nearsightedness- Myopia

• Light from a distant object is focused on the
  front of the retina

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Farsightedness- Hyperopia

• Light from an object or image close by is focused
  behind the retina
• Presbyopia during middle age, another form of
  farsightedness caused when the lens becomes
  brittle and inflexible

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Astigmatism

• An abnormally curved eyeball results in blurry
  vision for lines in a particular direction
• Corrected with glasses that intercept and bend
  the light so that the image falls properly on the
  retina

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The Retina

• A thin, light-sensitive membrane that lies at the
  back of the eye, covering most of its inner
  surface
• Contains two types of receptors for light rods
  and cones
• When exposed to light, rods and cones undergo a
  chemical reaction that results in a neural signal

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Rods

• Long and thin with blunt ends
• The eye contains about 125 million rods located
  in the outer edge of the retina
• Specialized function they are very sensitive to
  light
• We rely on them for our vision in dim light and
  at night

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Cones

• About 6 million per eye located in a small
  central region of the retina (fovea)
• Cones respond differently to different wave
  lengths, or colors, of light
• Responsible for color vision
• Each cone responds to either red, green, or blue
  wavelengths
• Cones are very sensitive to small features in the
  environment visual acuity

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Processing Visual Information-from the retina to
the brain

• Rods and cones connect to specialized neurons
  called bipolar cells
• The bipolar cells then funnel the collected raw
  data on to the ganglion cells
• Ganglion cells are specialized neurons
• There are one million ganglion cells

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How is the information transmitted from the
ganglion cells of the retina to the brain?

• The one million axons of the ganglion cells are
  bundled together to form the optic nerve, which
  carries messages from each eye to the brain
• The place where the axons of the ganglion cells
  join to form the optic nerve is called the blind
  spot an area that contains no photo receptors
  and is insensitive to light

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Optic Chiasm

• After the nerve fibers that make up the optic
  nerve leave the eyes, they separate, and some of
  them cross to the other side of the head at the
  optic chiasm.
• The nerve fibers from the right side of each eye
  travel to the right hemisphere of the brain
  those from the left side of the eye travel to the
  left hemisphere

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Neural pathways in the brain

• thalamus- processes information about form,
  color, brightness, and depth
• midbrain- processes information about the
  location of an object
• visual cortex processes information about form-
  such as angels, lines, movement and distance of
  objects

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Color Vision 3 Properties of Color

• Humans can see a range of colors
• 1.Hues different colors we see varies with the
  wavelength of light
• 2.Saturation vividness or richness of the hue
  (purity)
• 3.Brightness perceived intensity
• The color of an object is determined by the
  wavelength of light that the object reflects.

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Color and other species

• Many animals have some color vision
• Trichromats can see all hues-(humans, monkeys,
  apes)
• Dichromats can only see reds or greens, blues or
  yellows (most mammals)
• Monochromats completely color blind (reptiles,
  fish, insects, shellfish)

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Hearing

• Sound is air in motion
• When an object vibrates, it causes the air around
  it to move in waves
• Waves travel 700 MPH
• Humans detect vibrations of a frequency between
  30 and 20,000 hertz (cycles per second)

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3 Dimensions of Sound

• Pitch- determined by the frequency of sound
• Loudness- the result of the sounds intensity, or
  energy
• Timbre- the nature of the sound, or the shape

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The Ear Structure and Transduction

• The ear is divided into three areas outer,
  middle, inner
• OUTER EAR
• Sounds enters through flap- pinna
• Sounds travels through the air-filled auditory
  canal

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Middle Ear

• Sound enters middle ear hits tympanic membrane
  (eardrum) which vibrates with sound
• Behind the eardrum- 3 small bones- hammer, anvil,
  stirrup
• Stirrup vibrates onto the oval window, a membrane
  which covers an opening in the middle ear

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Inner Ear

• Cochlea- transmits auditory information, contains
  3 separate fluid-filled canals
• Canals spiral inside the cochlea, which wraps
  around like a snails shell
• Cochlea comprises the Corti- organ which contains
  auditory receptor cells

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Conductive Deafness

• Conductive deafness ear is not carrying sounds
  from the outer ear to the inner portion
• Bones of inner ear may be damaged, or
• may be an accumulation of dirt in the ear
• Person will be equally deaf to high and low tones

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Nerve Deafness

• Person has hard time hearing high -pitched tones
• Damage to the auditory nervous system
• Hair cells in the cochlea may be damaged- can no
  longer transduce vibrations of the cochlea fluid
  into neural impulses

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Touch

• Skin has 4 main senses of touch Cutaneous
  senses- cold, warmth, pressure, pain
• Free nerve fibers- responsible for temperature
  sensation- an increase in body temperature
  elicits a response
• Pressure-sensitive cells cells create receptor
  potentials when skin is bent or deformed
• Basket nerve ending structure that sense
  pressure at the roots of hairs
• Pacinian corpuscles respond when one feels deep
  pressure, such as in a massage

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Taste (Gustation)

• Taste receptors sensitive to sweet, sour,
  bitter, salty tastes
• Saliva- food enters mouth, mixes with liquid
• Solution flows into tiny holes in the tongue
  taste pores
• Each pore contains slim, hair like structures
  which are part of the taste bud
• When stimulated, receptor potential forms
• Nerves pass from tongue to the brain- tastes have
  different patterns of neural activity

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Smell (Olfaction)

• The sense of smell is entwined with taste
• Sense of smell can evoke distant memories and
  has connection to the temporal lobe
• Stimulus for smell is air-born chemicals
• Olfactory receptors- lie beneath nose in two
  patches of mucous membranes
• Chemicals in the air dissolve in the mucous and
  stimulate olfactory hair cells, cilia
• Olfactory mucosa- contains free nerve endings
  that sense noxious substances like ammonia

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Sensory Deprivation

• What would you do if you couldnt sense anything
  at all?
• Sensory deprivation studies
• 1. external stimuli kept to a minimum (sound
  proof room with no light)
• 2. changing or distorting the subjects
  environment (may hear a constant buzzing)
• 3. a monotonous environment, with no change in
  stimuli

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Sensory Deprivation in Adults

• Standard symptoms (depending on type of
  deprivation)
• Problems thinking clearly and concentrating, and
  score low on intelligence tests
• Difficulty counting above 20
• Hallucinate

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Sensory Deprivation in Infants

• When infants are deprived at critical stages of
  development, they may never develop normal
  abilities
• Orphanage babies vs. Nursing home babies