Rescorla-Wagner Model

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Rescorla-Wagner Model

• US-processing model

• Can account for some Pavlovian Conditioning
• phenomena

• acquisition

• blocking

• unblocking with an upshift

• conditioned inhibition

• US-pre-exposure effect

• Cannot account for some Pavlovian Conditioning
• phenomena

• extinction (i.e., spontaneous recovery)

• unblocking with a downshift

• latent inhibition

• temporal factors (i.e., CS-US interval)

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Pearce-Hall Model

• attention model of conditioning

• a CS-processing model

• according to the model, it is highly adaptive to
  pay
• pay attention to, or process, CSs that could
  become
• valid predictors of important outcomes (i.e., USs)

• it is also adaptive not to pay attention to, or
  process,
• CSs when the important event is already predicted
  by
• something else

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Pearce-Hall Model

• also based on the concept of surprise

• when the subject is surprised, attention to, or
• processing of the CS occurs

• as the US becomes predicted by a CS, and is less
  
• surprising, processing of the CS declines

• The amount of processing, that is associability
  of a CS,
• changes on each trial depending on whether the US
  was
• predicted (on the previous trial)

• If the US was predicted, then attention to the
  CS
• declines

• If the US was not predicted, then attention to
  the CS
• increases

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Pearce-Hall Model
?VA k(? VT)
Recall from the RW Model,
k constant salience or associability of the CS
With the PH Model, k changes across trials (CS
processing model, not a US processing model)
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Pearce-Hall Model
kAN ?N-1 VAN-1
kAN associative strength or associability of
CSA on trial N
?N-1 strength of the US on previous trial
VAN-1 strength of CSA on previous trial (could
become VT if more than one CS)
Important point k depends on what happened on
the previous trial on first exposure, novelty
causes some attention
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Pearce-Hall Model
kAN ?N-1 VAN-1
Early in training, when the strength of the CS is
low (i.e., ? V is high) see high k value and
thus, more attention to the CS
When the CS is strong in later trials (i.e., ?
V is small) attention to the CS is low
The important point is that attention to the CS
changes across trials
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Pearce-Hall Model
Attention to, or processing of, the CS can be
measured in terms of an OR (i.e., looking at a L)
This is different than the CR
Support for the PH Model comes from the finding
that subjects orient towards novel stimuli and
maintain their orientation, provided the
stimulus is a poor predictor of the US
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Kaye Pearce compared the OR in 3 groups of rats
Group 1
L alone
Group 2
L
condensed milk
Group 3
L
milk/no milk (inconsistent/random)
Looked at OR to L
Attention (OR) was high on the first trial since
the L is novel
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kAN ?N-1 VAN-1
Group 1 L alone
k stays low (decrease attention)
Group 2 L milk
VA gets bigger over time which makes the total
term smaller (this means small k and decrease in
attention)
Group 3 L milk/no milk
Attention remains high since VA is low
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When the CS is not a good predictor, rats
maintained their attention to the cue If the CS
is a good predictor (of the US or no US), then
attention decreases
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Pearce-Hall Model and Blocking

• like the RW Model, all CSs combine to predict
  the US

• if one CS already predicts the US, then pay less
  
• attention to all CSs on that trial

• when a new CS is added, should pay attention to
  it
• because it is novel

• therefore, should see some conditioning to the
  new cue
• on the first trial based on the salience of the CS

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Pearce-Hall Model and Blocking

• only after first trial is over would the animal
  know that
• nothing new had happened

• according to the model, should see blocking from
  trial
• 2 and onwards

• however, in most cases see blocking right from
  the start

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Pearce-Hall Model and Unblocking
kAN ?N-1 VAN-1

• when subjects encounter a US that is not well
  predicted,
• or is surprising (either bigger or smaller), then
  subjects
• should pay attention to all CSs on that trial and
  get
• unblocking

• because the formula includes the absolute value
  of
• ?N-1 VAN-1 it doesnt matter if the US is
  bigger or smaller

• if the US changes well see increase in
  attention and
• thus, learning

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Pearce-Hall Model and latent inhibition
When the CS is given by itself, see decrease in
attention to the CS over trials (? 0)
However, a problem with the model is that it
cannot explain the context-specificity of LI
If CS pre-exposures are given in one context, and
conditioning occurs in a second context, there
is no retardation of learning
According to the model, k should be low
regardless of context
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The Comparator Hypothesis

• developed by Ralph Miller

• this is a model of performance, not learning

• according to Miller, all CSs have excitatory
  power
• there is no separate inhibitory process

• the strength of performance (or CR) depends on
  the
• relative strength of the various excitatory
  associations

• a subject compares the excitatory strength of
  the
• explicit CS to the strength of other cues present
  in the
• situation, such as apparatus cues

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The Comparator Hypothesis

• when the strength of a CS is relatively greater
  than
• the background cues, get a measurable CR

• when the strength of a CS is weaker than the
• background cues, get weakened level of excitation
  (what
• others might call inhibition)

• according to the theory, the competition between
  two
• excitatory reactions controls performance

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The Comparator Hypothesis

• during normal excitatory, get CS-US pairings
  but
• the US is also paired with background cues and
  these
• background cues are the comparator stimuli

• because these background cues are also present
  during
• the no-US condition, they are typically weaker
  than
• the explicit CS

• so, under normal conditioning procedures, the CS
  has
• stronger excitatory strength than the comparator
  cues

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The Comparator Hypothesis

• during inhibitory conditioning, the CS is weak
  relative
• to the background cues

• during inhibitory conditioning, have CS no US
• pairings but the background cues are paired with
  the US
• and the absence of the US

• thus, the CS is weaker than the background cues
  and
• see little CR to the CS

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The Comparator Hypothesis

• Prediction After training one can manipulate
  the excitatory value of the context and this will
  affect the excitatory value of the CS
• E.g. After conditioning, give repeated exposure
  to the context alone followed by exposure to CS
• One will see greater responding to CS

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Temporal Factor Models

• designed to explain the effects of time in
  conditioning

• effects of time not considered in US-processing
  models
• like the RW model nor in CS-processing models
  like the
• PH model

• CS-US interval is one important temporal variable

• a more critical temporal variable appears to be
  the
• ratio of the ISI to ITI

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Midterm Exam Thursday, Feb. 17, 2005

• covers everything up to and including todays
  lecture
• in the case of a storm, the exam will take place
  during
• the very next class