 is something else that is solid. An awareness of the shape of objects and their locations in an ambient space is then developed on this basis. The “statue” subsequently learns to attribute smells and sounds to objects by discovering that moving objects can make these sensations appear or disappear (Treatise III.i-ii). Moving its hands before its eyes and discovering how this causes colour sensations to appear or disappear leads it to think of colour sensations at first as being on the surface of its eyes, then as being outside of it beyond arm's length, and then as being on the surfaces of particular tangible objects within arms length (Treatise III.iii.1–19). Having reached this stage of development, it is ready to learn to perceive objects to be at even more remote distances through discovering associations between such visual distance cues as the clarity and apparent size of visual images and the distance that must be crossed to touch an object. The interpretation of the cues then becomes so natural that we seem to be directly seeing depth. Condillac quietly ignored his earlier objections to this position (Treatise III.iii.20–33).
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).
Those perceptions that we attend to can seem to drown out the others and produce the illusion that they alone exist, whereas those perceptions that we are less conscious of can be so faint that it is impossible to recall that we have had them the instant after the stimulus that produced them fades. Those perceptions that we attend to can also continue for some time after the stimulus that produced them has ceased. This produces an experience that Condillac referred to as “reminiscence” (réminiscence). An object continuously acting on our sense organs causes us to now experience a particular perception while we are simultaneously conscious of an echo, as it were, of an identical past perception, produced just a moment ago. Condillac's reasoning is less than explicit at this point, but he seems to have taken this experience to provide us with an awareness of what we might call the “pastness” of the echo, and at the same time of the continued existence of an identical self which experienced both the past perception and the current ones. The idea of self is thus not the product of a Cartesian intellectual intuition. Like the idea of one's own extended body and of other extended things, it is discovered through having a particular kind of sensory experience, in this case, the experience of reminiscence (Essay I.ii.1. §15).
In the Essay, Condillac distinguished between reminiscence, understood as the perception that one is perceiving something that one has perceive