Cortical substrates of visuospatial awareness outside the classical dorsal stream of visual processing

This chapter presents work that addresses cortical substrates of visuospatial awareness outside the classical dorsal stream of visual processing. It is shown that the visual posterior sylvian area (VPS) may be a major player in a network of visual areas, underlying visual space perception and the subjective sense of visuospatial stability. This statement is based on experiments, which the authors have conducted in order to find an answer to the question of how the brain is able to construct a stable representation of the visual world, despite the confounding effects that movement of the subject has on the visual stimuli impinging on the retinas. The work clearly confirms the notion that the perception of visual motion is based on an inferential mechanism involving a nonretinal reference signal capturing the visual consequences of the eye movement. Furthermore, it illustrates that this inferential mechanism resides in rather ‘late’ parts of the cortical hierarchy of motion processing, sparing the early stages up to cortical area middle temporal (MT), and that disturbances of this mechanism may give rise to severe disturbances of vision and spatial orientation as exemplified by RW.