It is evident that this class of mnemonic illusions approximates in character to illusions of perception. When the imagination supplies the interpretation at the very time, and the mind reads this into the perceived object, the error is one of perception. When the addition is made afterwards, on reflecting upon the perception, the error is one of memory. The "fallacies of testimony" which depend on an adulteration of pure observation with inference and conjecture, as, for example, the inaccurate and wild statements of people respecting their experiences at spiritualist _seances_, while they illustrate the curious blending of both kinds of error, are probably much oftener illusions of memory than of perception.[125] Although in many cases we can account to ourselves for this confusion of fact and imagination, in other cases it is difficult to see any close relation between the fact remembered and the foreign element imported into it. An idea of memory seems sometimes to lose its proper moorings, so to speak; to drift about helplessly among other ideas, and finally, by some chance, to hook itself on to one of these, as though it naturally belonged to it. Anybody who has had an opportunity of carefully testing the truthfulness of his recollection of some remote event in early life will have found how oddly extraneous elements become incorporated into the memorial picture. Incidents get put into wrong places, the wrong persons are introduced into a scene, and so on. Here again we may illustrate the mnemonic illusion by a visual one. When a tree standing before or behind a house and projecting above or to the side of it is not sharply distinguished from the latter, it may serve to give it a very odd appearance. These confusions of the mental image may arise even when only a short interval has elapsed. In the case of many of the fleeting impressions that are only half recollected, this kind of error is very easy. Thus, for example, I may have lent a book to a friend last week. I really remember the act of lending it, but have forgotten the person. But I am not aware of this. The picture of memory has unknowingly to myself been filled up by this unconscious process of shifting and rearrangement, and the idea of another person has by some odd accident got substituted for that of the real borrower. If we could go deeply enough into the matter, we should, of course, be able to explain why this particular confusion arose. We might find, for example, that the two persons were associated in my mind by a link of resemblance, or that I had dealings with the other person about the same time. Similarly, when we manage to join an event to a wrong place, we may find that it is because we heard of the occurrence when staying at the particular locality, or in some other way had the image of the place closely associated in our minds with the event. But often we are wholly unable to explain the displacement.