The nature of intertheoretic relations between psychology and neuroscience is investigated. It is argued that more traditional views of such relationships fail to do justice to actual scientific practices and empirical developments. Research on vision in the cognitive neurosciences suggests a much more subtle and complex interplay. The case of vision shows mutual and continuous co-evolution of psychological and neurobiological theories, exemplifying the persisting top-down influences from psychology. It seems that discovering (or hypothesizing) the neural basis of functions does not eliminate the psychological approach, but, on the contrary, vindicates it. Many perceptual phenomena must be understood in terms of dynamical interactions between an observer and his/her environment. This means that internalist characterisations of the visual system must be supplemented with externalist accounts that address these reciprocal observer-environment interactions involved in vision. Such processes seem quite different from (internal) cellular and molecular ones, and as such seem to lie outside the scope of neuroscientific inquiry.