it is probable that what takes place is that one or several elements in the present situation are like those which had been experienced in the past, but that the dissimilarities in the situations are not observed. The individual has a memory defect in that he parallels or identifies a complex present experience with a similar complex past experience, although in the present experience the number of elements which are the same as those in the past may not be very great. In other words, the present experience is deemed to be the same as that of the past because of the fact that the past is not accurately remembered and properly localized in time.
Throughout all of these delusions one may discover that, in general, there are two ways in which they arise. As far as can be determined, Southard points out, the patients take data which are erroneous, such as the lack of sensation (anesthesia) and interpret the lack of normal sensation in a normal manner, viz., lack of sensation means that the part is missing. By a normal individual a different interpretation may be made, but the delusional interpretation is, it should be understood, equally logical. We may conclude, therefore, that delusions are sometimes due to the fact that abnormal sensory conditions are appropriately and logically interpreted. On the other hand, these delusions may also arise because of abnormal or faulty methods of interpreting the data which are correctly received by the patient. Thus, the woman who experienced a pain due to pleurisy did not say “I have a pain in my chest,” but “I have been shot in the chest.” In every case it is not always possible to determine whether the delusions are due to elements of abnormal data or elements of abnormal reasoning. It is possible that in every case both of these elements are to be found. As a rule, in those who are not mentally unbalanced anesthesias and pains do not lead to delusional interpretations. When the sciatic nerve has been cut in an otherwise normal individual the lack of sensations which are normally received from the foot and leg does not lead to the interpretation that the foot or leg has been cut off or is missing. Experiences through other channels of sense are added and are combined to interpret the phenomena in a normal manner. The leg exists, but it is not felt. The lack of feeling does, however, imply non-existence and this conclusion is most direct. Correction of this interpretation because of sensations obtained from other sources (e.g., the eye) are indirect. It is perfectly logical for the man suddenly stricken blind to believe that it has suddenly become dark. It is only by an extension of experience and by the utilization of other means of arriving at a conclusion that the logical interpretation gives way to what may be termed a “normal” interpretation. The formation of delusions as the result of abnormal modes of interpretation is probably most frequent.
