Vision has a dual life or possibly more. On the one hand, vision describes the environment as being a certain way. On the other hand, vision guides the execution of actions. Vision is, thus, Janus-faced : it is tied to both describing properties, this description being related also to spatial properties relevant for action, as well as to guiding the motor execution of that action. Philosophers and cognitive scientists have long studied this dual aspect of vision. However, this raises a fundament