Figure 2.

Graphical illustration of the hierarchical perceptual (generative) model with States x₁, x₂ and x₃. The probability at each level is determined by the variables and parameters at the level above. Each level relates to the level below by controlling the variance of its transition probability. The highest level in this hierarchy is a constant parameter, ϑ. At the first level, x₁ determines the probability of the input stimulus: standard (0) or deviant (1). The model parameters, ω and ϑ, control the agent’s belief update about State x. Note that setting κ = 0 effectively truncates the hierarchy to the first two levels. In the diagram, squares represent fixed parameters, while circles represent state variables that evolve in time.