Individual Differences and Dissociations in Category Learning (CL) Tasks Alan Pickering and Ian Tharp Department of Psychology a.pickering@gold.ac.uk

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)

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)

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

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

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

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

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

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

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

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

Task: After Kruschke (1993)

Results: Effects of IMPASS

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)

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

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

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)

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

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

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

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

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?

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

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)

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

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)

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

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

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)

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

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

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

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

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

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

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

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

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

II Task Structure

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

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

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

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

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)

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

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

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”

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

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

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