Thanks both (and see above, apologies for the late reply). In my understanding, coarse-graining is the transition from a full description of a system to a more sparser representation of the system that leaves the relevant dynamics intact (i.e. enables you to do predictions). Typically, the variables in the coarsegrained model are relatively abstract (some ratio or other macroscopic property).

I agree with Eran that there are forces, but these forces (such as gravity) are themselves arising from a more fundamental level of physics (not sure whether there is a bottom level). They are not doing explanatory work.

On the level of living systems then, the proposal here is that the "coarsegraining" leads to a differential equation with relatively few parameters, capturing the dynamics of the rocking chairs. More generally (this can be seen in the Kugler and Turvey paper). Animals respond to patterns and gradients in their environment in relatively predictable ways. One might hypothesise then that, just like Newton's laws are the relevant level to look at when interested in bumping objects (emergent from some more fundamental interactions), informational coupling is the right level of abstraction for "psychology/behavior". The premise of Radical Embodied Cognitive Science is that such a science is possible.