Implements Anderson (1991)'s rational model and a few of its successors.
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Rational models of categorization

Here are implemented several versions of the so-called rational model of categorization. Executing any of the python files here will launch a test/demo of one of these classic models.

All these models are essentially forms of the Dirichlet Process Mixture model with different posterior approximation methods. They assume that stimuli are generated by a mixture of underlying distributions of unknown size. These distributions are Gaussian on continuous stimulus dimensions, and multinomial on discrete stimulus dimensions. The prior over the number of mixture components is given via a Dirichlet distribution.


These should all run in Python >= 2.5, with numpy and scipy. The plotting in some of the demos will require matplotlib.

The original:

Anderson's original model is available here. In Figure 1 of Anderson (1991) [Anderson] walks through the model's inner workings on each time step as it learns the classic Medin & Schaffer (1978) [MedSchaff] task. Running the file in python launches a demo which performs the same task, finding the same answers at each step.

Becuase this model was developed before advanced techniques for approximating intractable Bayesian posteriors were in wide use, the model views stimuli sequentially and assigns them deterministically to the cluster that was most likely to have generated them.

[Anderson]Anderon, J. R. (1991). "The adaptive nature of human categorization." Psychological Review, 98:409-429.
[MedSchaff]Medin, D. L. and Schaffer, M. M. (1978). "Context Theory of Classification Learning." Psychological Review, 85:207-238.

The "more rational" model.

Recently, Sanborn, Griffiths and Navarro (2006) [sgn] brought the model up to date with two methods for approximating the full posterior over possible partitions of the stimuli. I have implemented the basic model in the document, and implemented each of these approximation methods as extensions. Since the Anderson model is a special use of the "more rational" model, it can also be run here. Psychologists are particularly interested in the particle filter because it operates on-line, which is generally taken as a necessity for a Psychologically plausible algorithm.

Gibbs Sampling
All items are assigned arbitrarily. Sampling proceeds by removing each item one by one and relabeling it probabilistically. In the limit, the likelihood of a given partition of the stimuli is given by the number of times it is visited. I have implemented this in Running the script launches a demo, which runs the sampler for a few hundred iterations on the Zeithamova and Maddox (2009) [zm] dataset, printing out its partition at each stage.
Particle filtering.
Items are viewed sequentially, as in the Anderson (1991) model, but the model tracks many hypotheses about the correct partition, and at each stage resamples from its own existing samples. I have implemented this in Running this script launches a demo which runs the [zm] task with 6 particles, plotting each particle's partition at the end.
[sgn]Sanborn, A. N., Griffiths T. L., and Navarro, D. J. (2006). "A More Rational Model of Categorization." Proceedings of the 28th Annual Conference of the Cognitive Science Society.
[zm](1, 2) Zeithamova, D. and Maddox, W. T. (2009). "Learning mode and exemplar sequencing in unsupervised category learning." Journal of Experimental Psychology: Learning, Memory, and Cognition, 35:731-757.


Although this is the codebase maintained by me (John McDonnell), it is highly intertwined with Doug Markant's implementation and can be considered to have been jointly authored, although as the maintainer, I take blame upon myself for any errors that have entered in.

No Warranty

I should also probably give the usual boilerplate about how this code is made available without any warranty of suitability for any particular purpose, authors are not responsible for disgraced careers, financial meltdowns, godzilla attacks, etc., that may arise from using it.