The Course's theory of perception, which is a reversal of the common sense belief that our perception is caused from without. External objects seem to be sending information through our senses to our brains, seemingly causing our perception of them. Yet our perceptions are caused internally. Over time we build up beliefs about reality. These beliefs guide our attention, causing our eyes to search for those things that fit our pre-existing categories (M-8.4). Once we find these things, our beliefs guide our interpretation of them, and these interpretations are our perceptions (see T-11.VI.1-3). Our perceptions are thus projections of our beliefs, through the means of selective attention and subjective interpretation. As a result, what we see is simply a mirror, a reflection of our state of mind. See perception, projection. See T-13.V.3:5, T-21.In.1:1.