This is the simplest sort of example that I was picturing as I wrote the suggestion - it might not be sophisticated enough as described below to be sufficiently challenging.

I also changed my mind a bit about how phase 1 should be structured, so I'll work that in.

A "scenario" is a box on the screen that is populated by colored shapes that move around like paramecia on a microscope slide, and interact with each other according to the rules for the current round of the game. The scenario ends after a short time period (20-40 seconds) and freezes in its End State. This is what the player will be trying to predict.

Phase 1: Several scenarios are presented in sequence. Each scenario consists of colored shapes interacting with one another - they might bounce off one another and change colors; they might split after a collision or spontaneously; they might eat one another, etc. The interactions show a pattern over the multiple scenarios, such that an observer will eventually start to form predictions about the end state of the system in each scenario. After the pattern has been demonstrated, the player could be asked to code a decision tree for prediction of the end state based on the pattern observed (or this step could actually be skipped, and the Phase 3 predictions just compared to the implicit ruleset used for the pattern without ever making sure the player knows it). Several more scenarios are presented where the player is asked to predict the final state (following the same ruleset as the earlier patterns).

A very simple example of such a ruleset could be as follows:

• If there are a circle and a square of the same color, they will collide.
• If a red circle collides with a red square, they will each split into two of themselves.
• If a blue circle collides with a blue square, the circle will 'eat' the square.
• If a circle and square of any other color collide, their states will not change after collision.

Phase 2: A given number of scenarios are presented (including the end state). This number is available to the player (ie, the player does not have to keep count of the total numbe (+ evidence). Some explicitly violate these rules (with varying degrees of blatancy - using the ruleset above, one scenario might contain only one pair of shapes that did follow the applicable rule, while another scenario might contain five pairs that misbehaved) (- evidence). Some contain shape/color combos that simply do not contain the right combinations to illustrate the rule (null evidence).

Phase 3: The player is asked to report the relative amounts of (+), (-), and (null) evidence presented in Phase 2.

There is one underlying ruleset per round of the game. Rounds can and should sometimes have rules that contradict rules from previous rounds. The rulesets increase in complexity each time a new round is begun.

Difficulty would increase with complexity of rulesets. Requiring the player to explicitly state the ruleset inferred in Phase 1 would probably make it easier. Introducing interacting symbols that have meaning beyond the bounds of the game (words or pictures) instead of the shapes would likely increase difficulty by requiring the player to ignore prior associations and biases attached to the symbols being used.

Does that make the idea a bit clearer?