Nature of Memory.—Mention has been made of the retentive power of the nervous system, and of a consequent tendency for mental images to revive, or re-present, themselves in consciousness. It must now be noted that such a re-presentation of former experiences is frequently accompanied with a distinct recognition that the present image or images have a definite reference to past time. In other words, the present mental fact is able to be placed in the midst of other events believed to make up some portion of our past experience. Such an ideal revival of a past experience, together with a recognition of the fact that it formerly occurred within our experience, is known as an act of memory.
Neural Conditions of Memory.—When any experience is thus reproduced, and recognized as a reproduction of a previous experience, there is physiologically a transmission of nervous energy through the same brain centres as were involved in the original experience. The mental reproduction of any image is conditioned, therefore, by the physical reproduction of a nervous impulse through a formerly established path. That this is possible is owing to the susceptibility of nervous tissue to take on habit, or to retain as permanent modifications, all impressions received. From this it is evident that when we say we retain certain facts in our mind, the statement is not in a sense true; for there is no knowledge stored up in consciousness as so many ideas. The statement is true, therefore, only in the sense that the mind is able to bring into consciousness a former experience by reinstating the necessary nervous impulses through the proper nervous arcs. What is actually retained, however, is the tendency to reinstate nervous movements through the same paths as were involved in the original experience. Although, therefore, retention is usually treated as a factor in memory, its basis is, in reality, physiological.
Memory Distinguished from Apperception.—The distinguishing characteristics of memory as a re-presentation in the mind of a former experience is evidently the mental attitude known as recognition. Memory, in other words, always implies a belief that the present mental state really represents a fact, or event, which formed a part of our past experience. In the apperceptive process as seen in an ordinary process of learning, on the other hand, although it seems to involve a re-presentation of former mental images in consciousness, this distinct reference of the revived imagery to past time is evidently wanting. When, for instance, the mind interprets a strange object as a pear-shaped, thin-rinded, many-seeded fruit, all these interpreting ideas are, in a sense, revivals of past experience; yet none carry with them any distinct reference to past time. In like manner, when I look at an object of a certain form and colour and say that it is a sweet apple, it is evidently owing to past experience that I can declare that particular object to be sweet. It is quite clear, however, that in such a case there is no distinct reference of the revived image of sweetness to any definite occurrence in one's former experience. Such an apperceptive revival, or re-presentation of past experience, because it includes merely a representation of mental images, but fails to relate them to the past, cannot be classed as an act of memory.
But Involves Apperceptive Process.—While, however, the mere revival of old knowledge in the apperceptive process does not constitute an act of memory, memory is itself only a special phase of the apperceptive process. When I think of a particular anecdote to-day, and say I remember having the same experience on Sunday evening last, the present mental images cannot be the very same images as were then experienced. The former images belonged to the past, while those at present in consciousness are a new creation, although dependent, as we have seen, upon certain physiological conditions established in the past. In an act of memory, therefore, the new presentation, like all new presentations, must be interpreted in terms of past experience, or by an apperceiving act of attention. Whenever in this apperceptive act there is, in addition to the interpretation, a further feeling, or sense, of familiarity, the presentation is accepted by the mind as a reproduction from past experience, or is recognized as belonging to the past. When, on the way down the street, for instance, impressions are received from a passing form, and a resulting act of apperceiving attention, besides reading meaning into them, awakens a sense of familiarity, the face is recognized as one seen on a former occasion. Memory, therefore, is a special mode of the apperceptive process of learning, and includes, in addition to the interpreting of the new through the old, a belief that there is an identity between the old and the new.
FACTORS OF MEMORY
In a complete example of memory the following factors may be noted:
1. The original presentation—as the first perception of an object or scene, the reading of a new story, the hearing of a particular voice, etc.
2. Retention—this involves the permanent changes wrought in the nervous tissue as a result of the presentation or learning process and, as mentioned above, is really physiological.
3. Recall—this implies the re-establishment of the nervous movements involved in the original experiences and an accompanying revival of the mental imagery.
4. Recognition—under this heading is included the sense of familiarity experienced in consciousness, and the consequent belief that the present experience actually occurred at some certain time as an element in our past experience.