Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Semantics and Pragmatics of Vision
A new paradigm for the study of human vision was introduced by the Canadian physiologist Melvyn Goodale and the British psychologist David Milner. They analyzed the visual pathways in the cerebral cortex (the "visual cortex") and realized that vision is actually a binary operation made of dual processes: on one hand is the conscious visual experience of the world, on the other hand is the visual control of unconscious (instinctive) action. They both require the eye as the organ, but they are functionally and structurally different processes.
Sensory information received from the eye diverges into two streams (two anatomically different pathways) when it leaves the visual cortex: a "ventral" stream flows from the primary visual cortex towards the inferior temporal lobe, while the "dorsal" stream flows from the primary visual cortex towards the posterior parietal lobe. This means that the ventral stream analyzes what object the eye is seeing, whereas the dorsal stream analyzes the spatial location of the object. In other words, the ventral stream is about recognition (e.g. of faces or objects) and conscious perception, whereas the dorsal stream is about automatic, unconscious action in space directed towards the object (typically action by the hand).
In a sense, there exist two kinds of vision: conscious perception and unconscious action. They are physically handled by two separate systems in the brain. There isn't a visual system: there are two visual systems that work parallel to each other.
Studying the difference between these two functional roles of the visual system, the French neurologist Marc Jeannerod had advanced the theory that there are two information processing systems for visual input: the "semantic processing system" (that yields a perceptual representation of the object) and the "pragmatic processing system" (that yields a motor representation of the same object).
The "dorsal" visual system that is common to most animals helps the animal carry out the orienting function: to detect movement (typically, either danger or food) and to guide action. The ventral visual system of the human brain is relatively distinct from the dorsal system and is related to the "semantic processing system" that analyzes and "recognizes" the object. This allows the human brain to carry out more sophisticated actions in response to a visual act. Human vision therefore originated when the functions of orientation and identification got separated.
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