Seeing and being aware of seeing require both intact visual perception and adequate insight of that perception itself. Patients with cerebral or acquired achromatopsia (color blindness) after damage of the color area (V4 and related visual areas on the ventral occipital cortex [18BA]) report to do not see colors and that the external world appears to them as either completely black or white and/or in gray tonalities with different brightness.
We published the case of a patient with achromatopsia (Carota & Calabrese., Case Rep Neurol 2013) who, despite affirming that he was not seeing any color, was able to recognize some colors with good accuracy and much more than what it is expected by mere chance. The condition of this patient corresponds to a form of agnosopsia (not knowing of seeing) and/or blindsight (blind vision) and/or to “superblindsight”.
Although this patient showed some confidence into the degree of his capacities of blind color recognition, he said that he was missing entirely that subjective universal mental state (the so called “qualia”) of colors for which “the color red is red!” as he saw all the world in gray tonalities. This patient reminds to the classical description of the philosophical zombie (p-zombie), which is a philosophical figure, a hypothetical non-human being, of which the behavior is indistinguishable from that of a normal human being except for the absence of conscious experience. When a p-zombie is confronted with the color “red”, it does not have the experience of “redness” but it behaves exactly as if seeing red.
The theoretical existence of p-zombies has been often advanced in philosophical discussions on the mind-body problem, usually against forms of behaviorism, to support the role of the subjective experience against the observable behavior. However, the phenomenon of patients with cerebral lesions and agnosopsia (as the case of my patient) gives, on the contrary, robust evidence to the conceivability of physical theories of the mind in order to account for those subjective “extra-sensorial” experiences that are not explicable or permeable to the knowing self.
In the future, functional neuroimaging studies should be specifically designed upon the exceptional cases of patients with color or other visual agnosopsias. Ad hoc experimental visual recognition paradigms focusing on activation/deactivation of brain areas in accord to the degree of confidence of the patient into his blind perceptions, could give further clues for the subjective and unconscious phenomenology of the “qualia” in the domains of the visual awareness and the general consciousness of the self.
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