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Individual Differences in Attention During Category Learning. Michael D. Lee UC Irvine. Ruud Wetzels University of Amsterdam. Kruschke (1993) Condensation Experiment. 8 stimuli varying in their box height and interior line position
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Individual Differences in Attention During Category Learning Michael D. LeeUC Irvine Ruud WetzelsUniversity of Amsterdam
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
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 …
Posterior Predictive • “Violin plots” of posterior predictive for each stimuli, together with aggregated data (black line) and individual data (broken lines)
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, …
Results of Individual Differences Analysis • Suggests there are two groups, with different attention
Bayes Factor • Savage-Dickey method gives approximate Bayes Factor of 2.3 in favor there being two groups (rather than one) “artist’s impression”
Posterior Predictive Distribution • Posterior predictive distributions of categorization behavior are qualitatively different • tracks people’s behavior at both the sub-group and individual level
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
Interpretation of Groups • The group on the left pays attention to position, and so makes mistakes with stimuli 4 and 5
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