 Condillac’s account of how sensation gives rise to the exercise of our higher cognitive faculties is broadly the same in the Essay and the Treatise. Such differences as there are between the two works arise from Condillac’s decision to focus the Treatise on pre-linguistic abilities. In the Essay Condillac defined perception as the impression first occasioned in the mind by the action of objects on the senses. He maintained that we are always conscious of perceptions, but that this consciousness comes in varying degrees, which are a function of the strength with which objects act on the senses, the degree of intrinsic painfulness or pleasantness of the perception, and, most importantly, the extent to which the perception has been associated with our needs, which are ultimately a function of the pleasure and pain we receive from our perceptions. A high degree of consciousness is what we call attention. Our attention is naturally drawn to those perceptions that are most pleasurable or painful, and consequently to those perceptions that we have connected with those that are most pleasurable or painful. Thus, experience of pleasure and pain is what first instructs us where to focus our attention. Learning where to focus attention is important, because many perceptions can be present at once, and a consciousness that is evenly distributed over a great number of perceptions knows none of them very clearly or distinctly (Essay I.ii.1. §§1–14). 