Significance of 4 stimulus cards in the Wisconsin Card Sorting Test? I've reviewed the papers by Grant, D. A., &amp; Berg, E. (1948) and Fey, E. T. (1951).

These papers from what I was able to find, lay out the basis of the Wisconsin Card Sorting Test (WCST). There are three possible rules for sorting the cards; color, shape, or count. I am curious why the WCST places 4 stimulus cards in front of the patient when 3 carefully chosen cards would be sufficient. With 4 cards it seems that unless the examiner makes special preparations, there might be occasions when there is more than 1 correct stimulus card to choose, or during a transition from certain rule to the next the patient may make an incorrect guess and won't be able to tell which rule to eliminate.

Can anyone explain why there has to be 4 stimulus cards? Could I run an equally effective WCST with 3 stimulus cards?


Grant, D. A., &amp; Berg, E. (1948). A behavioral analysis of degree of reinforcement and ease of shifting to new responses in a Weigl-type card-sorting problem. Journal of experimental psychology, 38(4), 404.
Fey, E. T. (1951). The performance of young schizophrenics and young normals on the Wisconsin Card Sorting Test. Journal of consulting psychology, 15(4), 311.
I cannot tell you why they chose four cards, but I do know that it is perfectly fine to use three, (e.g. Niv and colleagues, 2015).

To give you more info on why the WCST is used in the study by Niv. The study wanted to see how you could best model learning (and relearning) multidimensional information, to be able to better understand how people make sense of the multidimensional information provided by the real world. Therefore, they had participants perform the WCST with three cards. Multiple reinforcement learning algorithms were then fitted to the behavioral data, and they found that a reinforcement learning model that includes decay (as to model memory decay) was best able to do so. 

I believe it would have been perfectly fine to have used four cards in that study as well. It would make it more difficult to learn on which dimension to focus, which would probably also be modeled. 

There are also variations of the WCST (e.g. Catherwood and colleagues, 2014). In that study they instead of took apart four dimensions and showed a 2x2 matrix with each unit depicting a different dimension. 

In short

Depending on the goal of your experiment, you can decide how you would like to use the WCST specifically.