The passage suggests that all research has proven that which of the following is true about the phenomenon of synesthesia

(A) The lack of synesthetic color differences tends to hinder synesthetics in the same tasks where the presence of real color differences assists nonsynesthetes.
(B) The presence of real color differences tends to assist nonsynesthetes in the same tasks where the lack of synesthetic color differences assists synesthetes.
(C) The presence of synesthetic color differences tends to assist synesthetics in the same tasks where the presence of real color differences hinders nonsynesthetes.
(D) The lack of synesthetic color differences tends to hinder nonsynesthetes in the same tasks where the presence of real color differences assists synesthetes.
(E) The presence of real color differences tends to assist synesthetes in the same tasks where the lack of synesthetic color differences hinders nonsynesthetes.