ABSTRACT
Lower vertebrates possess brains that can be divided into three distinct regions that receive discrete sensory inputs. The development of the three major dorsal and ventral regions of grey matter in the brain of higher vertebrates passes through a stage that can be related to the regions of grey matter found in the brains of adult lower vertebrates. Since Homo sapiens are known to have consciousness, an inquiry into the evolution of consciousness is best begun by considering the primates closest to Homo sapiens. There are different forms of ‘blindness’ following different lesions to the visual pathway from the retina to the cortex. Removal of the cortex gives rise to a state of cortical blindness in which there is an absence of what would normally be called conscious visual sensations. Monkeys that have lesions in their primary visual cortex can learn to detect, localize and distinguish between visual stimuli presented within their visual field defects.
