Figure 5.

Natural transformation. Objects are Apples (A) and Berries (B) in categories C (central visual field) and E (entire visual field). Arrows in categories C and E are “nearly indistinguishable” in terms of color. Thus, category C is included in E. Central vision (C) is mapped to Left and Right visual fields by functor L and R, respectively, preserving objects and arrows. If natural transformation t exists from functor L to functor R, then indistinguishability of Left Apple to Right Berry can be established by both through Left Berry (=L(f);tB) or Right Apple (=tA;R(f)), that is, there is no path dependency. Note that tA is an arrow in category E, indicating that Apple in the Left is “nearly indistinguishable” from Apple in the Right. Same goes with tB for Berry in the Left and Right