As mentioned, type A and type B participants will complete slightly different versions of the decision task, and they will not do the tasks at the same time.
After the urns have been shuffled, first, each type A participant has to choose between the
two urns 4 times in a block before type B participants will face their decision task.
During these 4 rounds, the urns are not shuffled.
Every time a type A participant chooses an urn, a marble is randomly drawn from the chosen urn.
The colour of the marble is then revealed to the type A participant who has just chosen the urn.
Then, the colour of the marble is hidden again and it is put back into the same urn again.