The outward and inner powers.

In man five outer powers exist, which are the agents of perception, that is to say, through these five powers man perceives material beings.
These are sight, which perceives visible forms; hearing, which perceives audible sounds; smell, which perceives odors; taste, which perceives foods; and feeling, which is in all parts of the body, and perceives tangible things. These five powers perceive outward existences.
Man has also spiritual powers: imagination, which conceives things; thought, which reflects upon realities; comprehension, which comprehends realities, memory, which retains whatever man imagines, thinks, and comprehends.
The intermediary between the five outward powers and the inward powers, is the sense which they possess in common, that is to say, the sense which acts between the outer and inner powers, conveys to the inward powers  whatever the outer powers discern. It is termed the common faculty, because it communicates between the outward and inward powers, and thus is common to the outward and inward powers.

Selected Writings of Abdu’l-Bahá P.318