PSY 402

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PSY 402

• Theories of Learning
• Chapter 4 Theories of Conditioning

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Rescorla-Wagner Model

• Classical conditioning occurs only if the US
  (UCS) is surprising to the organism.
• If the UCS is already predicted by a CS, then it
  is not surprising it is expected.
• When the CS predicts the UCS perfectly, no
  further learning occurs.
• The asymptote (lambda, l) is the point where the
  learning levels off (no increase in learning
  occurs).

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Parts of the Model

• DV ab(l V)
• V is the Associative Strength (amount of
  learning).
• DV is the change in learning (increase in
  Associative Strength.
• a and b are the salience of the CS and UCS
• l V is the surprisingness of the US (the
  distance away from the asymptote).

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Multiple Conditioned Stimuli (CSs)

• The basic model explains changes in learning with
  one UCS and one CS.
• This doesnt explain what happens during blocking
  and unblocking, with multiple CSs.
• DV ab(l SV)
• When multiple CSs are present, SV is the sum of
  the associative strengths of all of the CSs
  (such as VN VL).

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Blocking

• First a noise is conditioned so that VN 1.0
• Next a light is added. The formula predicts its
  associative strength
• DVL ab(l SV)
• SV VN VL
• If we assume that ab .2 and VN is 0 because no
  learning has occurred yet, then
• DVL .21.0 (1.0 0) 0

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Unblocking

• As before, a noise is conditioned so that VN
  1.0
• A stronger US is presented with the new CS (VL).
• As before, the formula predicts its associative
  strength
• DVL ab(l SV)
• SV VN VL
• Again, we assume that ab .2 and VN is 0 but now
  the stronger US is 2.0 instead of 1.0
• DVL .22.0 (1.0 0) .21.0 .2

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Extinction

• During extinction, the CS is presented without
  the UCS.
• This is the same as presenting a UCS with
  intensity 0.
• The formula predicts the associative strength
  during extinction
• DVN ab(l V) but l is now 0 (due to
  extinction)
• DVN .20 1 -.2
• The associative strength is decreasing.
• Use the decreased value for VN (1-.2) for the
  next trial.

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Inhibition

• During inhibition, a second CSL is presented that
  has never been associated with the UCS (V 0).
• The formula predicts the associative strength for
  both CSs
• DVN ab(l SV) and DVL ab(l SV)
• DVN .20 (1.0 0) -.2
• DVL .20 (1.0 0) -.2
• V VN VL.

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Protection from Extinction

• When extinction of an excitor takes place
  together with extinction of an inhibitor, the
  excitor is never fully extinguished.
• This is called protection from extinction.
• To fully extinguish an excitor, and to extinguish
  it faster, pair it with another excitor (another
  CS associated with the US).
• The model predicts both of the these results.

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Overexpectation Effect

• The value of a model is that it predicts new
  findings.
• If you pair two previously conditioned CSs
  (excitors) on the same trial, V for each will
  decrease until SV equals l.
• This is because SV overexpects the UCS.
• Similarly, if a new CS (X) is added to the pair,
  it will become an inhibitor.

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Contextual Cues

• Contextual cues consist of everything in the
  environment in addition the CS and UCS.
• They cannot be ignored simply because the
  experimenter is not manipulating them.
• Whenever a CS or a UCS appears alone, it is
  still being paired with the context.
• When the context is considered another CS, then
  ideas about blocking explain learning.
• Zero contingency occurs because context is
  blocked.

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Comparator Theories

• An alternative theory to Rescorla-Wagner proposes
  that the CS and UCS are associated and the UCS
  and context are associated.
• The two sets of associations are compared to
  determine the amount of responding to the CS.
• The comparison determines the responding, not the
  learning.
• Strengthening or weakening the context, after
  learning, affects the amount of responding,
  supporting the theory.

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Problems with Rescorla-Wagner

• It predicts that presenting an inhibitory CS
  without the UCS should lead to extinction, but it
  doesnt.
• The model cannot account for latent inhibition
  (preexposure to the CS).
• Mackintosh demonstrated that animals learn to
  ignore redundant stimuli the model doesnt
  predict this learning.

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The Mackintosh Model

• Mackintosh proposed that the amount of learning
  depends on how much attention the animal pays to
  the CS.
• The attention to the CS is the a term in the
  Rescorla-Wagner model.
• Alpha increases when the CS is the best predictor
  and conditioning occurs to the best predictor of
  the UCS.

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Criticisms of the Mackintosh Model

• The model does a good job of explaining latent
  inhibition and its own criticisms of
  Rescorla-Wagner, but other problems arose.
• While attention is important, it doesnt
  necessarily increase when a CS becomes the best
  predictor.
• Hall Pearce showed that preexposure to a tone
  that was a good predictor of weak shock didnt
  help learning when a stronger shock was used.

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Conditioned Inhibition

• A CS can signal the presence of a UCS.
• This is called excitation, CS
• A CS that never appears with the UCS signals the
  absence of the UCS. It becomes an all clear
  signal.
• This is called inhibition, CS-
• In fear conditioning an excitor produces anxiety,
  an inhibitor produces relief or safety.

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Pearce Hall Model

• Animals dont waste attention on stimuli whose
  meaning is already well understood.
• Instead, they devote attention to understanding
  new stimuli.
• For their model, the value of alpha depends on
  how surprising the UCS was on the previous trial.
• If the UCS is surprising, the CS is not well
  understood. Alpha is high when this occurs.