Title: Integrating visual information through parallel pathways
Description: Visual information processing is both parallel and hierarchical, with each visual area richly interconnected with other visual areas. One example of the parallel architecture of the primate visual system is the existence of two major pathways providing input to the middle temporal visual area (MT): a direct projection from striate cortex (V1), and a set of indirect projections also originating in V1 but then relaying through V2 and V3. Here we ask whether these two different input pathways are redundant or whether they carry different kinds of information by reversibly inactivating the indirect pathway while recording from MT neurons and measuring eye movements in alert monkeys. We find that this inactivation causes a disproportionate degradation of binocular disparity tuning in MT neurons relative to direction tuning, suggesting that the indirect pathways play an important role in the recovery of depth in three-dimensional scenes. Single neurons integrate this depth information with information on motion provided by the direct pathway from V1, which might endow them with the ability to segregate motion signals arising from different depth planes.