Sensation and Perception'

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Sensation and Perception.

• HP502 Week 11.
• Dr Meredith McKague.

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Sensation and Perception

• This multitude of ideas, existing absolutely,
  yet clinging together, like dominoes in ceaseless
  change, or bits of glass in a kaleidoscope, -
  whence do they get their fantastic laws of
  clinging, and why do they cling in just the
  shapes they do?
• from The Principles of Psychology, James, 1890.

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What is reality?

• You assume it is what you see, hear, touch, taste
  and smell - but is this assumption justified?
• How does the nervous system translate information
  about the world into psychological experience?
• To what extent is our knowledge of the world
  given by experiences or constructed from
  experiences?
• To what extent do we need to learn how to
  perceive experience?

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What is Sensation?

• An internal representation of the stimulus
• The colour that you represent something to be,
  having taken into account the context.
• Sensations are the immediate experiences of
  qualities.

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What is perception?

• Perception is the process by which the brain
  organises and interprets sensations.
• Perceptions are experiences or events that appear
  to have form, order, meaning.

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Basic Principles.

• How many sensory modalities?
• Vision (sight)
• Audition (hearing)
• Touch
• Taste
• Olfaction (smell)
• Proprioception/Kinesthetic
• Other animals have other sensory modalities
  e.g. electromagnetic sharks, pigeons, bees, etc
• Senses are adaptations to our environment.

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Basic Principles Transduction.

• Transduction.
• The conversion of energy into internal signals
  that are psychologically meaningful.
• Sensation-perception-cognition.
• Sensory receptors (specialised neurons in each
  modality) transform energy into neural impulses
  that can be interpreted by the brain.

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Basic Principles Transduction

• Our conscious experience is determined less by
  the stimulus than by the particular neurons that
  are excited by it.
• Electrical stimulation of the visual sensory
  cortex produces the sensation of vision as surely
  as shining a light into the eye.
• The same stimulus to the auditory sensory cortex
  will produce the sensation of sound same
  stimulus, different experience.

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Basic principles Modality specific.

• Each sensory modality is subserved by a separate
  set of neural circuits (modules) that operate
  automatically and unconsciously.
• We are aware of nothing except the end product.

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Basic principles Thresholds.

• Absolute thresholds.
• The minimum amount of energy required for an
  observer to notice a stimulus.
• Signal detection.
• The detection of a signal against a background of
  noise.
• Noise is distracting information (can be
  internal or external).

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Basic Principles Response bias.

• Response bias.
• The observers confidence to report a sensation
  (decision criterion).

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Basic principles Response bias.

• To assess response bias researchers present
  participants with stimulus energy (the signal)
  and noise at low intensities.
• Some trials where there is no stimulus, just
  noise.
• Four kinds of responses.
• INCORRECT MISS FALSE ALARM
• CORRECT HIT CORRECT NEGATIVE

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Basic principles Response bias.

• Subjective can be influenced by expertise,
  expectancies and motivation.
• For example A doctors willingness to detect a
  tumor on a scan may be influenced by past
  experience (having missed one in the past, or
  having operated unnecessarily).

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Basic principles Difference thresholds.

• Difference thresholds.
• The lowest level of stimulation required to sense
  that a change in stimulation has occurred.
• The difference in intensity between two stimuli
  that is necessary to produce a just noticeable
  difference (JND).
• An absolute threshold is a special case of JND
  the difference between nothing and something.
• JND depends on the level of stimulation already
  present e.g. adding a 500 gram book to a
  backpack weighing 1kg vs to a backpack weighing
  30 kg.

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Basic principles Difference thresholds.

• Webers law, Fechners law and Stevens power
  law.
• Sensation has a lawful (orderly/predictable)
  relationship with physical stimulation, but
  psychological experience is not a copy of
  external reality.

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Basic principles Sensory adaptation.

• Sensory adaptation.
• The tendency of sensory receptors to respond less
  to stimuli that continue without change.
• Constant inputs provide no new information so the
  nervous system ignores them.
• Exceptions may adapt to mild pain, but not to
  severe pain.

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Sensation and consciousness.

• Something happens when to a certain brain state
  a certain consciousness corresponds. A genuine
  glimpse into what it is would be the scientific
  achievement before which all past achievements
  would pale.
• William James, 1899.

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Sensation and consciousness.

• William James
• Consciousness is the starting place of all
  psychology
• Consciousness is a non-entity and has no place
  among first principles.
• Mirrors the collapse of introspectionism and the
  rise of behaviourism.

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Sensation and consciousness Cartesian Dualism

• Sensory experience is at the heart of much of the
  western philosophical tradition of consciousness.
  
• Renee Descartes (1596-1650) I think therefore
  I am.

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Sensation and consciousness Cartesian Dualism

• I then examined closely what I was, and saw that
  I could imagine that there was no world, nor any
  place that I occupied, but that I could not
  imagine for a moment that I did not exist. On the
  very contrary, from the fact that I doubted the
  truth of other things, it followed very certainly
  that I existed.
• I concluded that I was a substance whose whole
  essence or nature was only to think, and which,
  to exist has no need of space nor of any material
  thing.
• It thus follows that this ego, this soulis
  entirely distinct from the body
• Rene Descartes (1637).

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Sensation and consciousness Cartesian Dualism

• Cartesian Dualism
• The view that the mind and the body are two
  separate substances
• Also known as substance dualism.
• res cogitans mental realm.
• res extensa physical realm
• Descartes proposed that the two substances
  interact via the Pineal Gland.

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Sensation and consciousness History in
psychology.

• Structuralism/Introspection.
• The fundamental assumption of introspection was
  that psychology was the study of the
  phenomenological mind.
• Aimed for a full description of the mental
  landscape as it appeared to the subject.

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Sensation and consciousness History in psychology

• Behaviourism.
• Scientific study of observable behaviour.
• Removal of states of consciousness seen as
  removing the barrier between psychological and
  natural sciences.
• Feigning anesthesia.
• It was great for you, how was it for me?

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Sensation and consciousness History in psychology

• Cognitivism.
• The success of cognitive psychology in explaining
  learning, memory and problem solving brings the
  issue of consciousness into stark relief.
• An unsolved anomaly within the paradigm.

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Sensation and consciousness History in psychology

• Consciousness becomes a box in a flow chart,
  e.g., Baddeleys Central Executive.
• Since Freud, consciousness was no longer the
  demarcation point between mind and not mind.
• Cognitivists tend to focus on the cognitive
  unconscious (e.g., Fodors modularity thesis).

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Sensation and consciousness History in psychology

• The treatment of consciousness as a functional
  processing stage is dissatisfying because it
  leaves out the phenomenal aspect of
  consciousness.
• Ironically , like the behaviourist, the
  cognitivist can also accused of feigning
  anesthesia.

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What is it like to be a bat? Qualia.

• Qualia The term used to refer to the feel of
  conscious experience
• what it is like to be x - where x is, for
  example, a human or a bat (Nagel).

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Qualia The feel of consciousness.

• The term quale refers to the particular sensory
  experience of some property e.g., warmth, pain,
  redness, the taste of chocolate.
• Consciousness reflects the integration of vast
  numbers of qualia to produce a succession of
  unified and integrated scenes - a stream of
  consciousness.
• The binding problem how is such unity created
  from separate brain modules??

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Absent Qualia and Zombies.

• A zombie is physically identical to a normal
  human being, but lacks conscious experience.
• There is nothing it is like to be a zombie.
• Why did evolution bother to produce us if zombies
  would have survived and reproduced just as well?

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Sensation and consciousness

• Consider what the following neurological
  conditions mean for your conscious sensory
  experience of the real world.
• Proposagnosia
• Loss of face recognition. The man who mistook his
  wife for a hat.
• Capgras delusion
• delusional belief that familiar people are
  imposters.
• Phantom limb
• cross-wiring of the sensory cortex as a function
  of amputation.
• Synesthesia
• cross-wiring of sensory modalities as a function
  of a genetic mutation (seeing numbers as
  coloured, tasting shapes, etc..
• Blindsight
• The ability to point accurately to an object that
  cannot be consciously seen. Damage to the visual
  cortex of one hemisphere leads to loss of vision
  for the opposite visual field.

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Penfields homunculus.
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Synesthesia.
Look at the top figure. Can you see the 2s? Look
at the bottom figure. This is how the top figure
appears to a synesthete who sees green 5s and
red 2s even when theyre black numbers. She
spots the 2s easily. Vilayanur S. Ramachandran,
University of California, San Diego
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Conscious sensation and mind time.

• Benjamin Libet has explored how cerebral nerve
  cell activities are involved in the production of
  conscious subjective experiences.
• If you tap your finger on the table you
  experience the event occurring in real time.
• However, Libets experiments indicate that the
  brain needs about half a second (500
  milliseconds) to produce awareness of the event.
• Our awareness of our sensory world is
  substantially delayed from its actual occurrence.
• Awareness is being distinguished from detection
  of a signal. Detection can occur unconsciously.

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Conscious sensation and mind time.

• Libets experiments use introspective reports
  from brain surgery patients while the cortex is
  stimulated with small electrical impulses.
• Patients awake with local anaesthetic applied to
  the scalp.
• Stimulation of the post-central gyrus
  (somatosensory cortex) produces a tingling
  sensation in corresponding body areas.
• Also used stimulation of skin and measurement of
  ERPs in the somatosensory cortex.

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Conscious sensation and mind time.

• Why do we feel as though we are immediately aware
  of events?
• How are we able to react to a sensory stimulus
  within 100 msec?
• What are the implications for the notion of free
  will in determining our behaviour?

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Some interesting reading

• Libet, B. (2004). Mind time. Harvard University
  Press.
• Ramachandran, V.S. (2004). A brief tour of human
  consciousness. PI Press.
• Sacks. O.W.S. (1985). The man who mistook his
  wife for a hat. Picador.