Visual processing.

(a) Schematic of visual processing across several areas defined by anatomical structure and function of the area such as V1, V2, V4, and Inferior Temporal cortex (IT). The major input to the visual cortex is from the lateral geniculate nucleus (LGN) whose principal neurons receive input from the retina [26]. (b) Models of the visual cortex. In feedforward models, information is only processed in one direction. In models with feedback connections, information from distant layers loops back to earlier layers (e.g. from IT to V1) across multiple distances [27]. Also, local activity feeds back to the same layer. (c) Feedforward models map each point in the input space to a point in the output space. In a model with feedback, a static point in the input space can generate a temporal dynamic (or trajectory) in the output space. The properties of the trajectory strongly depend on the feedback connections and the input. This image is inspired by Fig 2 in [28] describing “core vision”, the sub-second processing in primates during a single fixation.