Feedback connections and conscious vision

It is commonly thought that conscious perception of a visual stimulus is mediated by the arrival in the inferotemporal cortex of a wave of activation carried by feedforward connections from the visual cortical areas. A recent report of experiments using transcranial magnetic stimulation (TMS) challenges this view and shows instead that activation of the lowest cortical levels by feedback connections is necessary for conscious visual perception. This suggests that the lowest cortical stages act as 'active blackboards' for integrating the results of computations carried out in the different cortical areas of the visual system.