Visual cognition: a new look at the two-visual systems model.

In this paper, we argue that no valid comparison between visual representations can arise unless provision is made for three critical properties: their direction of fit, their direction of causation and the level of their conceptual content. The conceptual content in turn is a function of the level of processing. Representations arising from earlier stages of processing of visual input have very little or no conceptual content. Higher order representations get their conceptual content from the connections between visual cognition and other parts of the human cognitive system. The two other critical properties of visual representations are their mind/world direction of fit and their mind/world direction of causation. The output of the semantic processing of visual input has a full mind-to-world direction of fit and a full world-to-mind direction of causation: it visually registers the way the world is and is caused by what it represents. The output of the pragmatic processing yields information for the benefit of intentions, which clearly have a world-to-mind direction of fit and a mind-to-world direction of causation. An intention is both the representation of a goal and a cause of the transformation of a goal into a fact. These properties segregate representations specialized for perception from those specialized for action. Perception implies comparison between simultaneously represented and analyzed objects: hence, object perception presupposes the representation of spatial relationships among objects in a coordinate system independent from the perceiver. Spatial relationships carry cues for attributing meaning to an object, so that their processing is actually part of semantic processing of visual information. These considerations lead to a re-evaluation of the role of the two classical pathways of the human visual system: the ventral and the dorsal cortical pathways. The parietal lobe, which has been identified with the dorsal pathway, cannot be considered as a unitary entity with a single function. The superior parietal lobule carries visuomotor processing, a non-lateralized process. The right inferior parietal lobule contributes to the perception of spatial relationships, a process with a mind-to-world direction of fit and a world-to-mind direction of causation. Finally, the left inferior parietal lobule contributes to still another type of representation, related to visually goal-directed action, i.e., with both a world-to-mind direction of fit and a mind-to-world direction of causation.