1 / 13

Exploring Medin and Shaffer's Context Model: Structure and Probabilistic Framework

This document delves into Medin and Shaffer's Context Model, emphasizing its approach to categorization without relying on category information. It highlights the model's use of specific exemplars and how evidence for category A is derived from the likelihood of choosing exemplars based on similarity. Key aspects discussed include the significance of good matches versus weak matches, the role of dimension weights in categorization, and the effect of neural network models in relation to exemplar models. The research implications and relevance to acquired equivalence are also explored.

glenna
Download Presentation

Exploring Medin and Shaffer's Context Model: Structure and Probabilistic Framework

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Context Model, Bayesian Exemplar Models, Neural Networks

  2. Medin and Shaffer’s ‘Context Model’ • No category information -- only specific items or exemplars. • Evidence for category A given probe p: EA,p = Si in aS(p,i)/(Si in aS(p,i) + Siin bS(p,i)) • Where S(p,i) = Pj (Pj = Iij ? 1:aj) ; aj = c,f,s,p • Prob. of choosing category A given probe p: PA,p = EA,p

  3. Medin and Shaffer’s ‘Context Model’ • No category information -- only specific items or exemplars. • Evidence for category A given probe p: • EA,p = Si in aS(p,i)/(Si in aS(p,i) + Siin bS(p,i)) • Where • S(p,i) = Pj (Pj = Iij ? 1:aj) ; aj = c,f,s,p • Probability of choosing category A given probe p: • PA,p = EA,p

  4. Some things about the model • Good matches count more than weak matches • An exact match counts a lot • But many weak matches can work together to make a (non-presented) prototype come out better than any exemplar • Dimension weights like ‘effective distance’ (or maybe ‘log of effective distance?’ • If weight = 0, we get a categorical effect • Dimension weights are important – how are they determined? • Best fit to data? • Best choice to categorize examples correctly?

  5. Independent cue models For items 1, 2, 3 and 7:

  6. Neural Network Model Similar to Context Model Within each pool, units inhibit each other; between pools, they are mutually exictatory if neti(t) > 0 else Choice rule:

  7. What REMERGE Adds to Exemplar Models Recurrence allows similarity between stored items to influence performance, independent of direct activation by the probe. X

  8. Bayes/Exemplar-like Version of the Remerge Model inpi inpi Hedged softmax function: Logistic function: Choice rule:

  9. Acquired Equivalence(Shohamy & Wagner, 2008) • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4?

  10. Acquired Equivalence(Shohamy & Wagner, 2008) • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4? F1 S1 F2 S2 F3 S3 F4 S4

  11. Acquired Equivalence(Shohamy & Wagner, 2008) S1 S2 S3 S4 • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4? F1 S1 F2 S2 F3 S3 F4 S4

  12. Acquired Equivalence(Shohamy & Wagner, 2008) S1 S2 S3 S4 • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4? F1 S1 F2 S2 F3 S3 F4 S4

  13. Acquired Equivalence(Shohamy & Wagner, 2008) • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4?

More Related