Individual Differences and Dissociations in Category Learning CL Tasks

1
Individual Differences and Dissociations in
Category Learning (CL) Tasks

• Alan Pickering and Ian Tharp
• Department of Psychology
• a.pickering_at_gold.ac.uk

2
Collaborators

• Luke Smillie (University of Queensland)
• Rozmin Halari (Institute of Psychiatry)
• Lucy Schomberg, Debbie Benson, Fiona MacNab, and
  Wasima Ahmed
• (St Georges Hospital Medical School)

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Multiple Systems in CL?

• CL tasks may perhaps draw on 3 separate
  learning/memory systems
• Explicit verbalisable rule system
• prefrontal cortex
• Procedural (implicit) system
• basal ganglia
• Episodic memorisation (exemplar) system
• medial temporal lobes (MTL)

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Multiple Systems in Tasks
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CURRENT APPROACH

• Uses individual differences (esp. personality
  trait scores), in healthy subjects, as a tool for
  exploring dissociations in category learning (CL)
  tasks
• Looking for a characteristic individual
  differences signature for each different type of
  CL task

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Which Personality Traits?

• Extraversion-Introversion (EXT)
• Example measures EPQ-E Introvertive Anhedonia
  (IntAnh)
• Impulsive Antisocial Sensation Seeking (IMPASS)
• Example measures EPQ-P Novelty Seeking
  Sensation Seeking Scale
• Positive Schizotypy (SCHIZO)
• Example measures Unusual Experiences

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Example Questionnaire Items

• IMPASS Measure EPQ-P (25 items)
• -Have people said that you sometimes act
• too rashly?
• -Should people always respect the law?
• -Would you take drugs which may have
• strange or dangerous effects?
• Positive Schizotypy Measure Unusual
  Experiences (30 items)
• -I have felt that I have special, almost
• magical powers
• -Do you ever feel that your thoughts dont
• belong to you
• -Sometimes my thoughts are as real as
• actual events in my life

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Biological Basis of IMPASS Sample Evidence

• Gray, Pickering Gray (1994) SPET DA D2-binding
  in basal ganglia and EPQ-P

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Category Learning IMPASS Previous Work By
Others

• Ball Zuckerman (1990) positive correlation
  between Sensation Seeking scores and learning of
  a concept formation task
• Task likely to be rule-based but had relatively
  few exemplars and employed feedback

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Category Learning Personality Our Previous Work

• IMPASS traits correlated positively with CL
  performance in 2 studies with Kruschke (1993)
  task
• Results ambiguous task could be solved by a
  simple rule requiring selective attention to 1 of
  2 dimensions, but it had only 8 exemplars, and
  training involved feedback

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Category Learning IMPASS Study 1 with Ahmed

• A rule-based task (Kruschke, 1993)
• 2 stimulus dimensions one predicts category
  membership, other irrelevant
• Only 8 exemplars
• Training used verbal feedback
• N30 healthy male med. Students
• Measured IMPASS using Novelty Seeking Scale of
  Cloninger

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Task After Kruschke (1993)
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Results Effects of IMPASS
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Category Learning Personality Study 2
(Benson/MacNab)

• Same task (Kruschke, 1993) but with two phases
• N51 healthy med. students
• Measured IMPASS (EPQ-P) and SCHIZO (Unusual
  Experiences)

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Regression Results
R20.16 ?(IMPASS)0.29 ?(SCHIZO) -0.43
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Interpretation Conclusions 1

• IMPASS personality traits appear to be reliably
  related to CL task performance, and evidence for
  positive schizotypy traits too
• Unclear which learning system(s) may have been
  predominant in the task used.
• Further studies with careful task comparisons
  needed

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Category Learning Personality Our Previous Work

• Double dissociation found using matched tasks
  EXT was associated positively with task A but not
  B whereas reverse pattern was found for IMPASS.
• Task A encouraged use of procedural learning
  system (reinforcement no rule info integ
  structure probabilistic) whereas task B did not
  (paired-associate training without reinforcement)

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Study 3 (with Halari)

• Within-Ss design using 2 equivalent probabilistic
  category learning tasks Weather task and a
  Symptoms-Disease task
• Learning Regime (c/b across tasks, order)
• RF enhanced reinforcement
• 0.10 per correct response
• info. integration structure
• PA paired-associate training
• meant no reinforcement
• Testing
• Categorise each stimulus without reinforcement

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Category Learning in Parkinsons Disease

• Weather task Knowlton et al, 1996

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Details

• 40 healthy male participants, mostly students
• Personality Measures
• EXT Introvertive
• Anhedonia (IntAnh)
• IMPASS EPQ-P
• SCHIZO Unusual Experinces
• (UnEx)
• Dependent Variable Accuracy of responses during
  test

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Results Correlations

• RF reinforcement task score
• PA paired-associate task score

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Interpretation Conclusions 2

• Extraversion measures correlate with CL task
  performance where procedural system involvement
  is encouraged.
• Fits with neurobiological models of extraversion.
• IMPASS traits also correlate with CL task
  performance where procedural system involvement
  is unlikely. But why?

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Scanning to the rescue ?

• Poldrack et al 2001s fMRI study in healthy
  volunteers with weather task using standard
  feedback (FB) vs. paired associate (PA) training
• Medial temporal lobe (MTL) activity higher for PA
  than for FB task
• Reverse was true for basal ganglia (caudate
  nucleus) activity
• Maybe IMPASS correlation with PA task is mediated
  by episodic memory

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Category Learning Personality Our Previous Work

• Showed that IMPASS measures correlated positively
  with episodic memory performance in 2 studies.
• IMPASS measures also found to be correlated with
  behaviour on other tasks associated with
  hippocampal/MTL functioning (latent inhibtion
  response to associative mismatch)

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Study 4 IMPASS and Paired Associate Learning

• Pickering and Schomberg
• Unrelated verbal paired-associates (e.g.
  SOIL-MILE SIDE-BRAVE) were used
• This is the quintessential explicit memory task
  sensitive to hippocampal lesions
• 40 healthy subjects (students)
• Extraversion (Ext), IMPASS
• (EPQ-P), and positive schizotypy (UnEx) were
  measured

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ImpASS and Paired Associate Learning II

• 12 word pairs (A-B) used
• 3 study-test learning trials
• Test cued recall for B using A as cue
• 1 unexpected 10-min delayed cued recall test
  trial
• DVsNumber correct on each test (NC1, NC2, NC3,
  NCD)
• Measured IQ subtest performance for each subject
  (WAIS-III Matrices)

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IMPASS and Paired Associate Learning Results

• denotes correlation with EPQ-P after
• partialling out IQ

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Interpretation Conclusions 3

• IMPASS traits appear to be positively associated
  with performance on hippocampal-sensitive,
  episodic memory tasks
• The repeated positive correlation between IMPASS
  traits and CL task performance may therefore be
  indicative of the involvement of episodic memory
  processes on those tasks

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IMPASS and CL Study 5

• Study by Ian Tharp using matched information
  integration (II) and rule-based (RB) tasks from
  the Ashby/Maddox stable
• Counterbalanced withinSs design
• 16 training exemplars with feedback, trained to
  criterion
• 82 healthy subjects (mostly students)

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Ashby et al RB Task

• 1 dimension (background colour) determines
  category
• Readily verbalisable rule

Cat A
Cat B
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Ashby et al II Task

• 3 of the 4 dimensions determine categories
• Not readily verbalisable

Cat A
Cat B
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IMPASS CL Study 5 cont.

• Ss did 2 sessions one week apart
• 2 RB tasks in one session and 1 II task in the
  other
• Also measured paired-associate episodic memory as
  before and working memory performance in each
  subject
• Variety of personality measures

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Working Memory (WM) Task

• Memory set scanning task
• A set of 6 letters presented simultaneously for
  2.5 secs
• Y/N testing with 12 letters
• 10 sets used each quasi-randomly selected from 24
  letters (no O or L)
• Overall correct recorded

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Preliminary Results 1

• Regressions predicting CL correct

p0.06
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Preliminary Results 2

• Regressions predicting CL correct

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Preliminary Results 3

• Regressions predicting correct on II task

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Interpretation Conclusions 4

• Notionally II task strongly dependent on WM (more
  so than notionally RB task)
• Positive correlation between IMPASS and CL
  performance replicated reflects contribution of
  WM on task? (for rules or exemplars?)
• Negative relationship between positive schizotypy
  and CL performance also replicated and
  independent of WM

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IMPASS and CL Study 6

• Study by Ian Tharp using an information
  integration task from the Ashby/Maddox stable
• Stimuli were lines which varied in length and
  orientation
• 100 training exemplars with feedback, each
  presented twice
• 48 healthy male subjects (not all students)
• 4 different IMPASS measures

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II Task Structure
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Correlations with 4 IMPASS measures
Contrasts with previous 4 studies where
correlations were positive
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Preliminary Modelling 1

• Fit a General Linear Classifier model (i.e.,
  discriminant function D) to responses of each
  individual subject
• D b1length b2orient c0
• Relative values of b1 and b2 are informative
  w.r.t. task strategy
• unidimensional b1gtgtb2 or b2gtgtb1
• bidimensional b1 ? b2

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Preliminary Modelling 2

• Converted b1 and b2 into strategy index

BI
UNI
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Correlations with Strategy Index
A unidimensional strategy harms performance and
is favoured by high IMPASS subjects
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Interpretation Conclusions 5
Perhaps CL performance of high IMPASS Ss reflects
two distinct processes-

• Positive effect of involvement of
  working/episodic memory
• Effect of preference for simple unidimensional
  rules (can be positive or negative)

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IMPASS and CL Study 7

• Study with Luke Smillie
• Within-Ss design using 2 CL tasks
• Information integration Occupational Selection
  task
• Episodic memory task
• Good vs. Bad Numbers task
• 102 Australian psychology students
• 2 different IMPASS measures

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Numbers Task

• Quasi-randomly 6 2-digit numbers designated
  good and 6 2-digit numbers are designated bad
• Number selection avoids obvious rules
• Go vs. no-go responses with feedback
• Explicitly instructed to memorise
• 96 trials
• Predict positive correlation with IMPASS

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Occupational Selection Task OST

• S presented with ratings profiles of candidates
  on 5 job attributes
• S has to decide whether to hire
• 100 trials with feedback
• 50 suitable candidates who should be hired and 50
  unsuitable
• Instructed use only the ratings profiles, each
  attribute reliably but modestly related to
  suitability

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OST Stimuli and Predictions

• On each dimension, ratings were normally
  distributed
• Suitable mean 55 s.d. 18
• Unsuitable mean 40 s.d. 18
• Correlations between
• dimension and category 0.37-0.43
• dimensions 0.2-0.6
• Predict negative correlation with IMPASS

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OST Preliminary Results

• Correlations between task performance (d) and
  IMPASS

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General Conclusions

• Modest but reliable associations between
  personality traits and CL performance
• These relationships depend on type of CL task
  used in a relatively predictable way
• Findings contribute to the multiple systems view
  of CL performance