1. Individual Differences in Attention During Category Learning Michael D. Lee UC Irvine Ruud Wetzels University of Amsterdam

2. Kruschke (1993) Condensation Experiment  8 stimuli varying in their box height and interior line position  Divided into 2 categories, so that both dimensions are relevant  40 participants did 40 blocks of trials with corrective feedback

3. Generalized Context Model

4. Results of Standard GCM Analysis  Marginal posterior over the attention parameter indicates both dimensions are important  Familiar story, and a strong temptation to stop there …

5. Posterior Predictive  “Violin plots” of posterior predictive for each stimuli, together with aggregated data (black line) and individual data (broken lines)

6. Types of Individual Differences

7. Allowing for Individual Differences  Continuous individual differences are modeled by drawing subject parameters from an over-arching hierarchical distribution  Discrete individual differences are modeled as a latent mixture, so different subjects can be drawn from different group distributions  Let WinBUGS do the heavy lifting, check chains for convergence, etc, …

8. Results of Individual Differences Analysis  Suggests there are two groups, with different attention

9. Bayes Factor  Savage-Dickey method gives approximate Bayes Factor of 2.3 in favor there being two groups (rather than one) “artist’s impression”

10. Posterior Predictive Distribution  Posterior predictive distributions of categorization behavior are qualitatively different  tracks people’s behavior at both the sub-group and individual level

11. Interpretation of Groups  The two groups are shown in the panels  The bars show the number of “A” vs “B” category decisions made for each stimulus

12. Interpretation of Groups  The group on the left pays attention to position, and so makes mistakes with stimuli 4 and 5

13. Interpretation of Groups  The group on the left pays attention to position, and so makes mistakes with stimuli 4 and 5  The group on the right pays attention to height, and so makes mistakes with stimuli 2 and 7