I was using "percieve" with the definition "to become aware of directly through any of the senses, especially sight or hearing." I wouldn't say we perceive memory, but that we are or become conscious or, to put it another way, aware of it. Once an event has completed and is no longer being perceived, it becomes only memory and thus subject to imagination and degradation.

Memory is fallible and never wholly accurate, so we determine its validity inductively. There are many things to consider: the possibility of the memory's content; the credibility of the person with the memory; how well the memory stacks up to relevant evidence; and how often the memory contradicts the testimonies of others concerning the same event. All this will lead to a probability of the memory's truthfullness; however, absolute certainty is unobtainable.

This implies that insanity is a willful distancing from common perceptions of reality; I wholly disagree with this since it denies those who struggle with mental illnesses such as manic depression and schizophrenia, illnesses which they neither cultivated for themselves or wish to retain. Often times their only respite comes from external stimulus, sensory or chemical, such a psychiatry (sensory) and medication (chemical). Which suggests not only that the mind does not control the external world, but that the external world very much controls our individual minds.