Sensation and Perception

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Sensation and Perception

• Lecturer Doneisha Burke, MS.c

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Sensation

• The study of sensation is concerned with the
  initial contact between organisms and their
  physical environment.
• Focus is on describing the relationship between
  various forms of sensory stimulation ( sound
  waves, pressure) and how these inputs are
  registered by our sense organs
• Sensory Receptors are cells of the body
  specialized for the task of transduction.

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Sensation

• How are the many forms of physical energy
  impacting our sensory systems converted into
  signals our nervous system can understand?
• Sensory receptors
• Cells of the body specialized for converting
  physical energy into neural impulses that are
  then transmitted to our brain (eye, ears, tongue,
  nose)

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Sensation How much Stimulation is Enough?

• Sensory Deprivation
• When deprived of all sensory input our bodies
  produce hallucinations to fill the void.
• Our detection level for sensory input is
  impressively low for most aspects of sensation
• Although our receptors are highly efficient they
  do not register all information in the
  environment at any given moment.

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Sensation How much Stimulation is Enough?

• In investigating the sensory capabilities of the
  various sense organs psychologists have sought to
  establish the r-ship between physical properties
  of stimuli (e.g brightness and loudness) and
  peoples psychological experience of them.
• Our sensitivity to stimuli changes from moment to
  moment as the bodys need to maintain homeostasis
  changes

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Sensation How much Stimulation is Enough?

• In response to these changes the term absolute
  threshold the smallest amount of a stimulus that
  we can detect 50 of the time-has been coined to
  denote our sensory threshold.

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Sensation How much Stimulation is Enough?

• In order to measure the sensitivity of our
  sensory organs Psychophysical Procedures are used
  they include
• The Method of Limits
• Employs the use of a series of ascending and
  descending trials. Both trials are rptd several
  times to provide a reliable estimate of the
  threshold.

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Sensation How much Stimulation is Enough?

• The Staircase Method
• Experimenter begins with a descending series
  until the person reports not hearing a sound then
  switches to an ascending series until the person
  indicates hearing the sound.
• The Method of Constant Stimuli
• The range of sound intensities to be tested are
  selected in advance and each tone is presented
  many times in an irregular order i.e some sounds
  are at, above or below the threshold.
  Participants respond yes/no.

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Sensation How much Stimulation is Enough?

• Sensory thresholds are not really fixed, i.e it
  changes with lapses in attention, fatigue etc. It
  has also been suggested that motivational factors
  play a role.
• Signal Detection Theory supports this claim
• Theory suggesting that are no absolute thresholds
  for sensations. Rather, detection of stimuli
  depends on their physical energy and on internal
  and motivational factors associated with
  detecting their presence.

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Sensation How much Stimulation is Enough?

• How much change in a stimulus is needed before a
  shift can be noticed?
• Difference Threshold
• The amount by which 2 stimuli must differ in
  order to be just noticeably different and the
  smaller the change we can detect then the greater
  our sensitivity.

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Sensation How much Stimulation is Enough?

• Stimuli below the Threshold/Subliminal Perception
• The presumed ability to perceive a stimulus that
  is below the threshold for conscious experience.
• This speaks to the use of subliminal messages.
• Research indicates no evidence to support that
  subliminal messages are a powerful means of
  persuasion

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Sensation How much Stimulation is Enough?

• Sensory Adaptation is the reduced sensitivity to
  unchanging stimuli over time.
• It helps us to adapt and focus on important
  changes in the world around us key to
  survivalblinking, swallowing, the feel of our
  tongue in our mouth
• Danger! It can lessen sensitivity

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Vision The Eye

• Light energy is converted into signals our brain
  can understand as a result of the eye.
• It is here that light energy is converted into
  neural codes which our nervous system can
  understand.
• Cornea-gtPupil-gtIris-gtLens-gtRetina-gtCones (Fovea)
  Rods-gtBipolar cells-gtGanglion Cells-gtOptic
  nerve which carries visual information to the
  brain. (pg 93)

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Vision The Process

• Light rays first pass through the cornea and
  enter the eye through the pupil whose size varies
  with lighting conditions. The iris is responsible
  for regulating the contracting and expanding of
  the pupil to let in varying amounts of light.
  From here light rays pass through the lens which
  allows us to focus on objects of varying
  distance. Light rays which leave the lens are
  then projected onto the retina at the back of the
  eyeball.

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Vision The Eye
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Vision The Eye

• Cornea- transparent structure through which light
  rays enter the eye.
• Pupil- An opening Located just behind the cornea
  through which light rays enter the eye.
• Iris- Coloured part of the eye which adjusts the
  amount of light entering the eye by dilating or
  constricting.
• Lens- Curved structure behind the pupil that
  bends light rays focusing them on the retina.

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Vision The Eye

• Retina- Surface on the back of the eye containing
  the rods and cones.
• Cones- Sensory receptors located in the Fovea
  that play a crucial role in seeing in bright
  light, colour recognition and our ability to
  notice fine detail (apprx. 5 mil)
• Rods- found outside the Fovea, they help us to
  see in a darkened room or at night (apprx 120
  mil)
• Fovea- Area in the centre of the Retina in which
  Cones are highly concentrated.

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Vision The Eye

• Optic Nerve- A bundle of nerve fibres that exit
  the back of the eye and carry visual information
  to the brain.
• Blind Spot- The point in the back of the Retina
  through which the optic nerve exist the eye. This
  exit point contains no rods or cones and
  therefore insensitive to light.

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Vision The Eye

• Acuity, the visual ability to see fine detail, is
  an important aspect of vision.
• Persons who are near/far sighted suffer from
  visual deficits in the shape of their eye or
  cornea and wear glasses to correct this.
• Dark Adaptation, the increase in sensitivity
  which occurs when we move from bright light to a
  dim environment.

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Vision The Eye

• Point of Information- Nearly 8 of men and 0.4
  of women are less sensitive than the rest of us
  either to red and green or to yellow and blue.
• Colour Blindness in which the world is
  experienced in only varying shades of black and
  gray.

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Vision The Eye

• Visual Disorders
• Blindsight- damage to visual cortex in which
  persons report being blind yet respond to certain
  visual stimuli.
• Prosopagnosia- rare condition in which brain
  damage impairs a persons ability to recognize
  faces.

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Hearing The Ear

• Inside the ear is an intricate system of
  membranes, small bones and receptor cells that
  transform sound waves into neural information for
  the brain.

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Hearing The Ear

• Pinna- The visible part of our hearing organ.
• Eardrum- A thin piece tissue just inside the ear
  , which moves ever so slightly to sound waves
  striking it.
• Cochlea- Fluid filled spiral shaped structure of
  the inner ear containing the sensory receptors
  for sound.

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Hearing The Ear

• But how exactly do we hear?
• Sound waves enter through the external auditory
  canal and produce slight movements which cause
  the middle ear bones to vibrate. The fluid within
  the COCHLEA then moves resulting in tiny HAIR
  CELLS (the sensory receptors for sound) located
  in the BASILAR MEMBRANE shifting their position
  thereby generating nerve impulses which we
  perceive as sound. These nerve impulses are
  transmitted to the brain via the auditory nerve.

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Hearing The Ear
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Hearing The Ear

• Physical Psychological Qualities of Sound
• Loudness
• Refers to amplitudes of sound waves, so as
  amplitude increase the sound appears louder.
• Pitch
• It is determined by the frequency of the sound
  waves that pass a given point/ secs.
• Timbre
• The quality of the sound we perceive which helps
  us to distinguish a flute from a trumpet.

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Hearing The Ear

• Detecting differences in Pitch
• Place Theory (Traveling Wave Theory)
• Theory suggesting that sounds of different
  frequencies cause different places along the
  basilar membrane to vibrate.
• Frequency Theory
• Theory suggesting that sounds of different pitch
  cause different rates of neural firing i.e high
  pitch sounds produce high rates of activity in
  the auditory nerve and vice versa.

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Hearing The Ear

• Sound Localization- How do I know where to turn
  my head?
• LOCALIZATION is the ability of the auditory
  system to locate the direction of a sound source.
• Sound from the side vs. the front or back.

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Hearing The Ear

• Hearing Loss is a result of damage to the sensory
  receptors for hearing i.e the tiny hair cells
  that line the floor of the basilar membrane.
• To measure hearing loss psychologists measure
  hearing thresholds at various sound freq. before
  and after exposure to sounds of certain
  intensity.

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Hearing The Ear

• Decibels in Everyday Life
• Whisper- 30dB
• Ringing phone-80dB
• Normal Convo- 60dB
• Prolonged exposure to Decibel Levels above 90 can
  produce permanent hearing loss
• Gunshot 165dB
• Ambulance Siren 120dB
• Headset on high 112dB
• Deploying Airbag 170dB

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Smell Taste

• Why study them together?
• Both respond to substances in solution (chemical
  sense) i.e substances that have been dissolved in
  fluid or gas.
• In everyday life both are interrelated.
• The stimulus for smell consist of molecules of
  various substances located in the air.

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Smell

• Odorants enter the nasal passage and dissolve in
  the moist nasal tissues. This brings them into
  contact with receptor cells found in the
  olfactory epithelium.
• You and I have about 50 mil vs. cats and dogs
  with gt200 mil

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Smell

• Our sense of smell is restricted in terms of the
  range of stimuli to which they are sensitive,
  Why?
• Answer- In order for our olfactory sense to
  detect odours there has to be molecular weight
  (btw 15-300), that is why we can smell vodka (46)
  in a mixed drink and not the table sugar (342).

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Taste

• The sensory receptors for taste are located in
  the small bumps on the tongue i.e PAPILLAE.
• Each PAPILLAE contains a cluster of taste buds
  possessing several receptor cells.
• Humans 10,000
• Chickens 24
• Catfish gt175,000 over the surface of their body.
• How many tastes are humans able to distinguish
  and what are they?

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Taste

• Sweet
• Salty
• Sour
• Bitter
• Why then does it seem like we identify more?

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Taste

• Not only are we aware of taste, but smell,
  texture, temperature, the pressure exerted on our
  tongue and mouth and many more other sensations.
• If these are however removed all we have are the
  4- sweet, salty, sour and bitter.

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Did you know?

• Tip of the nose phenomenon.
• Anosmia.
• Our memory of odours are impressive.
• Aromatherapy lavender, cedar, peppermint and
  lemon.

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Kinesthesia Vestibular Sense

• 2 critical and often times ignored aspects of our
  sensory system.
• Kinesthesia-the sense that gives us information
  about location of our body parts with respect to
  one another and allows us to perform movement.
  E.g. touching your nose with your fingertip to
  driving a car.
• Kinesthetic information comes from receptors in
  our joints, ligaments muscle fibres. Also
  vision and touch.

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Kinesthesia Vestibular Sense

• Vestibular Sense- refers to our sense of balance,
  It gives us information about body position,
  movement and acceleration (critical to S.o.B.)
• Sensory Receptors are located in the inner ear.
  i.e the 2 fluid filled Vestibular Sacs.
• They provide information about the bodys
  position in relation to the earth by tracking
  changes in linear movement.

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Kinesthesia Vestibular Sense

• When we move our bodies e.g.. Tilting the head
  from side to side hair cells bend in proportion
  to the rate of change in our motion. It is this
  movement that causes attached nerve fibres to
  fire neural signals which are then sent to the
  brain.

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Kinesthesia Vestibular Sense

• When do we become aware of our vestibular sense?
• After activities which make us dizzy.
• Vestibular information also comes from other
  senses esp. vision.
• When the two are in conflict it can lead to
  motion sickness.

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The Somatosenses (Pain, Touch Temperature)

• Did you know that the skin is our largest sensory
  organ?
• There are several skin senses
• Touch/pressure
• Warmth
• Cold
• Pain
• Why are certain areas of your body more sensitive
  than others?

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The Somatosenses (Pain, Touch Temperature

• Answer receptors in our skin are not evenly
  distributed
• Face and fingers are more sensitive than legs
  because receptors are much more densely packed.
• Psychologists distinguish between 2 types of
  touch
• Passive vs. Active
• Object comes in contact with the skin vice
  versa.

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Pain Perception

• Pain sensation has no specific stimulus, however
  the sensation of pain originates in free nerve
  endings located throughout the body in the skin,
  around muscles and in internal organs.
• 2 types of pain exist
• Quick and sharp- what we feel from a cut.
• Dull and throbbing- what we feel from a sore
  muscle/back injury.

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Pain Perception

• Gate Control Theory- a theory suggesting that the
  spinal cord contains mechanisms that can block
  transmission of pain to the brain
• Pain messages carried by the large fibres cause
  the gate to close whereas messages carried by the
  small fibres do not.
• This can help to explain why sharp pain is
  relatively brief and dull pain the opposite.

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Pain Perception

• This theory also helps to explain why vigorous
  stimulation of an area succeeds in reducing pain.
• So using an ice pack, rubbing the skin near the
  injury or even acupuncture can have a soothing
  effect as it stimulates activities in the large
  nerve fibres which close the gate and reduces
  pain. This is known as a counter measure.

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Pain perception

• Other factors which affect our perception of pain
  include
• Current emotional states
• Culture (physical difference in pain threshold
  vs. social learning)
• Cognitive processes
• Pain causes a shift in thought and behaviour
  thereby redirecting our attention to the pain.

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Pain Perception the role of cognitive processes

• The extent to which we experience pain results
  from an interplay btw 2 factors.
• Characteristics related to pain
• The context in which the pain emerges
• Cognition/thought appears to play a critical
  mediator role which determines the extent to
  which we focus on pain relative to these factors.
• Procedures that redirect attention are therefore
  effective countermeasures

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Pain Perception the role of cognitive processes

• Hypnosis
• Cognitive behavioural procedures
• Based on the notion that our thoughts, feelings
  and beliefs can dramatically influence our
  perceptions of pain.
• Positive vs. negative thought
• Beliefs
• (page 106)

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Perception Putting it all together

• Transmission of sensory information from sensory
  receptors to the brain is only part of the
  picture.
• Of equal importance is PERCEPTION- the way in
  which we select, organize and interpret sensory
  input to achieve a grasp of our surroundings.

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Perception Attention

• When you are engrossed in a good book, a movie or
  even a phone conversation, what do you notice
  happens?
• By shifting attention what then happens?
• The reason you were not aware before is that we
  cannot absorb all of the available sensory
  information in our environment.
• That is why we SELECTIVELY ATTEND- paying
  attention to certain aspects of our environment
  while putting less important aspects in the
  background.

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Perception Attention

• Selective Attention has advantages and
  disadvantages such as
• Can you shut out everything?
• The cocktail party phenomenon
• Certain characteristics of stimuli can cause
  attention to shift suddenly e.g. novelty, colour,
  sudden change.
• This ability is critical to survival as it alerts
  us to immediate dangers in our environment.

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The Plasticity of Perception

• This refers to the extent to which perception is
  innate or learned.
• Innate
• 2 lines of research support this side.
• Persons born without sight/ loose it shortly
  after birth and then have it restored can in fact
  make at least partial sense out of the visual
  world soon after regaining sight. For e.g. they
  can follow moving objects.

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The Plasticity of Perception

• Research with young babies a few hours old
  suggest that numerous perceptual abilities
  (auditory visual) are present at birth.
• Learned
• Kittens raised in darkness except for being
  exposed to vertical and horizontal stripes.
• Recent research shows that organisms are able to
  compensate for deficits through enhanced
  abilities in their other senses.

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Extra Sensory perception

• Can we gain information about the external world
  without use of our 5 basic senses?
• ESP- perception without a basis in sensory input
• Does it really exist? Bem and Honorton have
  recast this question in terms of a hypothetical
  process known a Psi.

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Extra Sensory perception

• Psi- Unusual processes of information or energy
  transfer that are currently unexplained in terms
  of known physical or biological mechanisms.
• Parapsychologists suggest that there are actually
  several distinct forms of psi
• Precognition
• Clairvoyance
• Telepathy
• Psychokinesis

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Extra Sensory perception

• Precognition- the ability to foretell future
  events
• Clairvoyance- the ability to perceive objects or
  events that do not directly stimulate your
  sensory organs.
• Telepathy- the direct transmission of thought
  from one person to the next.
• Psychokinesis- the ability to affect the physical
  world purely through thought.

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Extra Sensory perception

• Does it really exist?
• Failure to replicate instances of psi
• All aspects of our behaviour must ultimately stem
  from biochemical events of which none appears to
  account for psi.
• Evidence for support comes from persons deeply
  convinced of its existence.