Human and non-human primates possess exquisitely sensitive depth processing that aids their ability to perceive and interact with objects in a three-dimensional environment. Simple actions like grasping an object involve complex cerebral mechanisms that not only provide information about the distance of the object relative to the point of ocular fixation but also combine it with an estimate of the viewing distance to recover the real metric depth of the object. Little is known about how and where the brain encodes viewing distance in a reference system centred on the body and how this information is used to encode object depth. A current theory supposes that real depth could be obtained from a change, produced by extra-retinal signals, in the gain response of disparity neurons. This proposal will focus on the influence of vergence signals on depth encoding in humans and monkeys.To examine both the similarities and differences between the neural mechanisms involved in the two species, we will use the same experimental protocols and perform functional magnetic resonance imaging (fMRI) measurements. We will characterize the activation within well-defined functional areas and use state-of-art classification methods based on multi-voxel pattern analysis (MVPA). Additional fMRI recordings on monkeys will be performed using a new de-activation cooling technique to assess the causal influence of vergence signals on real-depth encoding. The advanced imaging facilities in the host institution and the concentration of world experts in 3D vision make it an optimal location for the proposed study.The research project has multiple potential applications in robotics or clinical abnormalities such as amblyopia and also 3D video enhancement. It is therefore of interest for a wide range of scientists in fields including neuroscience, medicine, engineering and species evolution. It will contribute to building new connections between the European Research Area and the United States.