I. Introduction
The primate visual pathway propagates visual input from the eye to the brain. Information travels from the retina in the eye to the lateral geniculate nucleus (LGN), then to the primary visual area (V1) in the cortex, secondary visual area (V2), and so on. However, massive amounts of connections in the reverse direction (i.e. internal feedback pathways, or IFPs) are also observed, as shown in Fig. 1. These connections are known by a variety of names in neuroscientific literature, including descending feedback, predictive feedback, reciprocal connections, and recurrence. Feedback is well-documented but poorly understood [3]–[5]; understanding the purpose of this mechanism is invaluable to understanding overall circuit function in the visual system.