1. Individual Differences and Dissociations in Category Learning (CL) Tasks
Alan Pickering and Ian Tharp
Department of Psychology

2. Collaborators Luke Smillie (University of Queensland)
Rozmin Halari (Institute of Psychiatry)
Lucy Schomberg, Debbie Benson, Fiona MacNab, and Wasima Ahmed
(St George’s Hospital Medical School)

3. 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)

4. Multiple Systems in Tasks
Key process
Deployed in CL tasks with:
Rule-based
Working
memory
many exemplars; verbalisable rule;
irrel. dimensions
Procedural
Reinforce-ment
many exemplars;
no rule; feedback;
info integration
Episodic
Exemplar
storage / retrieval
few exemplars; no rule

5. 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

6. 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

7. 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 don’t
belong to you
-Sometimes my thoughts are as real as
actual events in my life

8. Biological Basis of IMPASS: Sample Evidence
Gray, Pickering & Gray (1994): SPET DA D2-binding in basal ganglia and EPQ-P

9. 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

10. 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

11. 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
N=30 healthy male med. Students
Measured IMPASS using Novelty Seeking Scale of Cloninger

12. Task: After Kruschke (1993)

13. Results: Effects of IMPASS

14. Category Learning & Personality: Study 2 (Benson/MacNab)
Same task (Kruschke, 1993) but with two phases
N=51 healthy med. students
Measured IMPASS (EPQ-P) and SCHIZO (Unusual Experiences)

15. Regression Results
R2=0.16; (IMPASS)=0.29; (SCHIZO)= -0.43

16. 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

17. 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)

18. 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

19. Category Learning in Parkinson’s Disease
Weather task: Knowlton et al, 1996

20. 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

21. Results: Correlations
RF= reinforcement task score
PA= paired-associate task score
SCHIZO
EXT
IMPASS RF
UnEx
IntAnh
EPQ-P PA
0.14
-0.01
-0.06
0.30*
0.20
-0.35*
0.00
0.02
0.34*
0.13

22. 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?

23. Scanning to the rescue …?
Poldrack et al 2001’s 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

24. 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)

25. 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

26. 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
DVs=Number correct on each test (NC1, NC2, NC3, & NCD)
Measured IQ subtest performance for each subject (WAIS-III Matrices)

27. IMPASS and Paired Associate Learning: Results
EXT
IMP
ASS
ASS*
SCHIZO IQ
NC1
0.17
0.43
0.40
0.15
0.26
NC2
-0.03
0.33
0.29
0.09
0.28
NC3
-0.10
0.08
0.27
NCD
-0.04
0.37
0.35
-0.01
*denotes correlation with EPQ-P after
partialling out IQ

28. 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

29. 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 within–Ss design
16 training exemplars with feedback, trained to criterion
82 healthy subjects (mostly students)

30. Ashby et al: RB Task
1 dimension (background colour) determines category
Readily verbalisable rule
Cat A
Cat B

31. Ashby et al: II Task 3 of the 4 dimensions determine categories
Not readily verbalisable
Cat A
Cat B

32. 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

33. 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

34. Preliminary Results 1 Regressions predicting CL %correct  IMPASS
SCHIZO
RB1
0.06
-0.11
RB2
0.11 II
0.17†
-0.20*
† p=0.06

35. Preliminary Results 2 Regressions predicting CL %correct  WM %corr
PA #corr
RB1
0.07
0.14
RB2
0.04
0.19* II
0.37**
-0.05

36. Preliminary Results 3 Regressions predicting %correct on II task: 
IMPASS
SCHIZO
WM %corr PA
#corr
0.13
-0.20*
0.33**
0.02

37. 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

38. 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

39. II Task Structure

40. Correlations with 4 IMPASS measures
IMPNON
EPQ-P
SSS
BAS-FS
% Corr
-0.32*
-0.17
-0.30*
-0.27
Contrasts with previous 4 studies where correlations were positive

41. Preliminary Modelling 1
Fit a “General Linear Classifier” model (i.e., discriminant function D) to responses of each individual subject
D = b1*length + b2*orient + c0
Relative values of b1 and b2 are informative w.r.t. task strategy
unidimensional b1>>b2 or b2>>b1
bidimensional b1  b2

42. Preliminary Modelling 2
Converted b1 and b2 into strategy index BI
UNI

43. Correlations with Strategy Index
IMP-NON
EPQ-P
SSS
BAS-FS
Strat. Index
-0.51**
0.26
0.31*
0.23
0.16
A unidimensional strategy harms performance and is favoured by high IMPASS subjects

44. 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)

45. 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

46. 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

47. 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”

48. 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
dimensions
Predict negative correlation with IMPASS

49. OST: Preliminary Results
Correlations between task performance (d’) and IMPASS
EPQ-P
EPP-SS
Numbersd’
0.16*
OST d’
-0.14*

50. 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