首楞嚴義疏注經 4.562

4.562

此則近以世人六根隔越不相通用，尚有知覺同者，豈況真覺須假根塵耶？六根無辨故云黯然，頭足不分故云相類。若以手摸頭足，明辨與見無異，故云知覺是同。

This draws a proximate example from worldly people whose six faculties are divided and do not function interchangeably, yet their awareness is still the same; how much more so with true awareness—must it rely on faculties and dusts? Because the six faculties cannot discern, it says "dim and obscure"; because head and feet are not differentiated, it says "seem alike." If one uses a hand to touch head and feet, discerning them clearly is no different from seeing; hence it says "knowing and perceiving are the same."