§ 10. Facilitation and Arrest.—In actual reproduction, one mental process reinstates another. But instead of actual reinstatement, we may have mere facilitation. The one mental process may favour the entrance of the other into consciousness, without actually introducing it into consciousness.

Facilitation may assume many forms and take place under many diverse conditions. It is an essential characteristic of attention. The nurse whose attention is concentrated on the sick child is predisposed to notice whatever sign or movement it makes, and to take action accordingly. Her mind is set in a general attitude of response to whatever impressions come to her from this source. This general attitude of response to a certain kind of stimulus may persist even when conscious attention has itself ceased. The nurse who goes to sleep with her attention concentrated on the child is likely to be awakened by the slightest cry from it, though more intense sounds fail to disturb her repose.

Under the head of facilitation due to attention we may bring a fact noticed by Mr. Verdon in a very interesting paper on ''Forgetfulness."'* ''Individuals often remember clearly and well up to the time when they have to use their knowledge, and then, when it is no longer required, there follows a rapid and extensive decay of the traces. Many schoolboys forget their lessons after they have said them; many barristers forget details got up for a particular case. Thus, a boy learns thirty lines of Homer, says them perfectly, and then forgets them so that he could not say five consecutive lines the next morning, and a barrister may be one week learned in the mysteries of making cogwheels, but in the next he may be well acquainted with the anatomy of the ribs instead." In other words, the general direction of interest facilitates the recall of certain experiences. It makes the corresponding dispositions more readily excitable. This seems only partially to depend on direct attention to the special subjectmatter to be remembered. The barrister who keeps in mind for a week "the mysteries of making cogwheels" does so through general interest in the case which he has in hand, and not by constantly thinking of cogwheels. In other words, the corresponding mental dispositions are maintained in an excitable condition, not so much by attending directly to the subject matter, as by attending to something connected with it. So long as the need for remembering remains, there is a sense of having something on the mind. When the need no longer exists, a feeling of relief is experienced, and the power of remembering disappears.

*Mind, 0,S, ii., 449.

If we learn something by heart, e.g., a page of verse, we may afterwards so far forget it as to be unable to recall the words in their proper order. We may then set about learning it anew. But on the second occasion it may take very much less time to do so than on the first. The original learning by heart has facilitated the second.

The nature of facilitation is well illustrated in a series of experiments carried out by Professor Pillsbury.* Printed words variously misspelt were successively exposed on a screen for a period of about onefifth of a second. The subject of the experiment was called on to read off these words. He did so for the most part incorrectly, and most often without noticing the wrong spelling. We have here nothing to do with the nature and frequency of the mistakes. What does interest us is the effect produced by calling out a word having some association with the word to be shown immediately before the exposure was made. The result of this was always a great increase in the number of misspellings overlooked. "In only a very few cases did the word called out suggest the word to be shown before the latter was seen, and then the misprints were observed quite as frequently as at other times. In most cases, the relation between the two words was noted after the printed word was seen. In such cases, the association helped the entrance of the word. It seemed to confirm the results of the visual impression, and to give a feeling of confidence that the word seen was the word intended." The words called, though they did not of themselves actually reproduce other words, yet facilitated the perception of one word rather than of another.

Arrest may be regarded as the negative side of facilitation. Whatever facilitates the occurrence of certain mental processes is a bar to the occurrence of others. The nurse, with attention concentrated on the child, is apt to overlook impressions which are not connected with the main direction of her interest. In general, any mental process tends to hinder the occurrence of others, if and so far as it does not facilitate their occurrence.

* •• A Study in Apperception," American Journal of Psychology, viii. 3.