I led Gordon Holmes and Aleksander Luria to propose that the posterior parietal association area was responsible for definition of an extra- personal space. Ungerleider and Mishkin extended this early work by making a series of discrete lesions in the visual areas of monkeys. This has permitted subdivision of the posterior parietal association into a number of sub-regions. Sequential and parallel processing of visual information has been documented along these visual pathways. Note that cells in the ventral pathway of the visual system are sensitive to the outline of images, their orientation and their boundaries.
All cells are capable of very high resolution of detail.
Note that inactivation of the parvo- or magnocellular portions of the LGN demonstrated that these pathways are NOT completely segregated. Responses of cells in area MT were always reduced or eliminated after inactivation of the magnocellular layer. This suggests that despite the beautiful anatomy demonstrated above, V4 neurons are dependent on both P and M cell input. The cells in both the ventral and dorsal streams have been studied using sophisticated, neurophysiologic techniques in awake, behaving monkeys. These cells are organized in direction columns that run perpendicular to the surface of the cortex.