Efforts to use seldom seen people as sensors of one’s own changes in cognitive function are complicated by the fact that observations of changes in one’s appearance trump those of subtler changes by virtue of being easier to articulate and obliging what is nothing short of a social expectation. This would be a point undeserving of attention if it weren’t for the tendency of subtle changes to have larger implications than their more obvious counterparts.

In this arena, sight reins over the other senses; first, due to the straightforward dependence of time-static appearance on the eyes, and second, because the only changes in cognitive function that can be sensed by others are those which manifest themselves as changes in behavior, and detecting changes in behavior relies mostly on time-dynamic visual observation. Though odd, it’s reasonable, then, on a fundamental level, to equate changes in behavior to nothing more than “time-dynamic appearance variance” (i.e. changes in appearance over a continuous interval of time). It’s rather like stacking a number of time-static appearance cards chronologically in a deck and then flipping through them like a flip book, giving rise to the illusion of motion and rendering the deck as a whole time-dynamic; the difference here being that it isn’t the motion (read: behavior) itself that is of interest, but changes in the motion.

As previously explained, people often won’t overtly express observations of the time-dynamic sort, especially if these observations are interpreted negatively, so if one wants to glean insight from sensors standing near, one must resort to sensing others’ sensing of oneself. This is obviously a poor mechanism for self-evaluation, not only on account of being at a distance twice removed, but also because one is inextricably linked to bias. Despite these failings, its continued use is motivated by there being too few alternatives, superior or otherwise.