One dominant thesis is that different properties of the visual world (color, motion, form and so forth) require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
[14] Thus the current evidence suggests that motion processing occurs in a modular stream, although with a role in form and depth perception at higher levels.
The well studied patient DF is unable to recognize or discriminate objects[49] owing to damage in areas of the lateral occipital cortex although she can see scenes without problem – she can literally see the forest but not the trees.
However, other evidence that shows a tight coupling of perceptual and physiological changes[52] suggests activation in this area does underpin object recognition.
[55] Perhaps some of the strongest evidence for the modular nature of these processing systems is the double dissociation between object- and face (prosop-) agnosia.
However, as with color and motion, early areas (see [46] for a comprehensive review) are implicated too, lending support to the idea of a multistage stream terminating in the inferotemporal cortex rather than an isolated module.
That these streams have the same implementation in early visual areas, like V1, is not inconsistent with a modular viewpoint: to adopt the canonical analogy in cognition, it is possible for different software to run on the same hardware.
[24][25] In addition, although achromats experience other cognitive defects[59] they do not have motion deficits when their lesion is restricted to V4, or total loss of form perception.
Furthermore, that the intensity of subjective perceptual experience (e.g. color) correlates with activity in these specific areas (e.g. V4),[33] the recent evidence that synaesthetes show V4 activation during the perceptual experience of color, as well as the fact that damage to these areas results in concomitant behavioral deficits (the processing may be occurring but perceivers do not have access to the information) are all evidence for visual modularity.