Learning in Hybrid Active Inference Models

An open problem in artificial intelligence is how systems can flexibly learn discrete abstractions that are useful for solving inherently continuous problems. Previous work in computational neuroscience has considered this functional integration of discrete and continuous variables during decision-making under the formalism of active inference [13,29]. However, their focus is on the expressive physical implementation of categorical decisions and the hierarchical mixed generative model is assumed to be known. As a consequence, it is unclear how this framework might be extended to the learning of appropriate coarse-grained variables for a given task. In light of this, we present a novel hierarchical hybrid active inference agent in which a high-level discrete active inference planner sits above a low-level continuous active inference controller. We make use of recent work in recurrent switching linear dynamical systems (rSLDS) which learn meaningful discrete representations of complex continuous dynamics via piecewise linear decomposition [22]. The representations learnt by the rSLDS inform the structure of the hybrid decision-making agent and allow us to (1) lift decision-making into the discrete domain enabling us to exploit information-theoretic exploration bonuses (2) specify temporally-abstracted sub-goals in a method reminiscent of the options framework [34] and (3) 'cache' the approximate solutions to low-level problems in the discrete planner. We apply our model to the sparse Continuous Mountain Car task, demonstrating fast system identification via enhanced exploration and successful planning through the delineation of abstract sub-goals.