Three points for today

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Three points for today
Sensory memory (SM) contains highly transient
information about the dynamic sensory
array. Stabilizing the contents of SM allows
identification of external stimuli, which in turn
permits access to knowledge. Stabilization
produces a new experience of world, that we call
consciousness.
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Header
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1. The world and our representation of it.

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The world and our representation of it
A. External world Dynamic (in motion with
respect to us). That is, something is always
happening. B. Internal representation of the
world Begins with receptor surface.
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Question
Can the receptor surface drive all
responses? That is, can any response be both
prompted and guided only by information available
at the receptor surface? E.g., shadow passing
over squirrel causes squirrel to run for shelter
without thinking.
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Which behaviours could be driven by receptors?
Responses based on distinctions available at
receptors e.g., for vision light
intensity wavelength (hue) contrast Nothing
involving learning.
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Which responses cannot be driven by receptors?
Responses based on abstract properties for
vision, these properties would include size s
hape category name These properties are
computed based on information extracted from SM.
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• How do we extract information about objects from
  sensory memory?
• Two issues
• 1. What is the nature of the stimulus
  representation?
• 2. How does the extraction process work?
• Which question is logically prior?

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• What is the nature of the stimulus
  representation?
• Three suggestions, in historical order
• Template theory
• Feature theory
• Structural description theory

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• Template theory
• memory contains pictures of (whole) objects
• stimulus representations are also pictures of
  objects
• recognition involves searching memory for
  picture that matches current stimulus
  representation.

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• Problem with Template theory
• How do you recognize objects at an unfamiliar
  orientation?

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• Feature theory
• all visual objects are composed of features
• stored representations are lists of features
• stimulus representation created by extracting
  features from visual object
• recognition consists of matching feature sets

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• Problems with feature theory
• What are the features?
• nobody knows
• 2. What about spatial relations among features?

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Chair?
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Structural Descriptions A feature theory with
spatial relations among features specified in
description. Biedermans Recognition by
Components theory Geons geometric ions
(primitives)
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In column B, the geons can be recovered, so the
objects can be identified. Not so in column C.
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How does the extraction process work? 1. Source
- sensory memory Duration capacity 2.
Destination - short term memory 3. Rumelharts
model
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• Sensory memory
• Sperling (1960)
• Tachistoscopic procedure
• very brief exposure of a visual array
• subjects task is to report whats in the array.
• - until Sperling, whole report technique used.

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• Whole report
• report all letters on screen
• 4 or 5 items out of 12 correct
• Were those 4 or 5 all there was in SM?
• Did the rest decay during read-out?

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Theory 1 thats all we can get into SM
J V E C M B S A Y L K R
J V E C M
J V E C M
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Theory 2 rest of array decays during read-out
J V E C M B S A Y L K R
J V E C M B S A Y L K R
J V E C M
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J V E C M B S A Y L K R

Thats all I remember
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Sperling (1960) Partial report technique After
display disappears, a tone signals which row to
report. Logic if you can report a randomly
selected row, you could have reported the other
rows, too if a different tone had sounded.
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Hear Report High tone top row Medium
tone middle row Low tone bottom row
J V E C M B S A Y L K R
Note delay between display offset and tone onset
variable. Basic effect delay 0 msec.
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• Sperlings results
• 76 correct in partial report condition.
• Result suggests that most of a complex display is
  available in SM immediately after offset.
• 76 of 4 letters 3 letters. Why not 4 or 5 as
  in whole report condition?
• After 5 seconds, most of array has decayed.

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• Rumelharts model
• Model of the extraction process that takes
  information from SM to STM. Explains Sperlings
  results.
• Process operates in parallel on all contents of
  SM (unless task instructions say focus).
• Process influenced by stimulus quality better
  quality, faster process.

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J V E C M B S A Y L K R
Process operates in parallel. Process influenced
by stimulus quality.
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• As a result, we can recognize thousands of
  objects.
• We have many possible responses to each object.
• How do we select
• which object we should respond to?
• which response to that object we should carry
  out?

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Selection is the responsibility of attention
see next chapter. But note William
James Selection is the function of
consciousness. Consciousness refers to
experiencing the world.
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Which comes first? Do we have consciousness
because we have stable representations? Or do we
have stable representations because we have
consciousness (so are able to choose objects and
responses)?
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• Quick evaluation
• On a piece of paper, please write down one or two
  sentences about each of
• What you liked best about todays lecture.
• What you still have some confusion about.
• Be constructive but dont put your name on the
  paper! (Please hand it in as you leave.)