Graphical description of a two-state Hidden Markov Model.

At any point in time the prawn is in a state of either CW or anti-CW orientation. The precise state is hidden but we make observations , the actual frame-by-frame movements of the prawn, which give information about the relative probabilities of the two states. We assume a fixed probability of transition between the states which is inferred from the data and allows for the persistence of orientation over time.