Sensation

Sensation is the lowest level of consciousness, in the words of Peikoff, sensations are "irreducible state[s] of awareness produced by the action of a stimulus on a sense organ."^[1] "Irreducible" because a sensation cannot be broken down into simpler conscious units---there are not turtles all the way down, sensations are the root of all awareness. "Produced by" because sensations are not primaries---under a certain set of circumstances a sense organ will cause certain effects. For instance, when a ray of light hits the retina of your eye, the relevant cells will inexorably send a signal to your brain representing some colour; similarly, when sound waves vibrate your ear drum there is a sensation of sound at a certain pitch. What this means is that there is no choice involved on the sensory level---you cannot control the operation of your sense organs, unlike your conceptual faculty.

Another important point, implicit in the above, is that a sensation lasts only as long as the sensory stimulus is maintained---your eye ball will stop sending colour signals the instant the light is no longer entering it. To do otherwise would mean to have an effect without a cause---which is a violation of the law of causality.

The most primitive conscious organisms appear to possess only the capacity of sensation. The conscious life of such organisms is the experience of isolated, fleeting data---fleeting, because the organisms are bombarded by a flux of stimuli. These creatures confront a kaleidoscopic succession of new worlds, each swept away by the next as the stimuli involved fade or change. Since such consciousnesses do not retain their mental contents, they can hardly detect relationships among them. To such mentalities, the universe is, in William James's apt description, a "blooming, buzzing confusion."^[2]