or irregularly distributed intervals would be unfavorable, and the effect of the latter, which is to produce a lengthening of the reaction time, may be regarded as a detraction effect. If the explanation that I have given of their effect is correct, it is evident that in the case of the irregular procedure, where perception of time does not enter as a factor, we are dealing with a very pure form of detraction from attention. That is, the prolongation in reaction time is due to the fact that we place the subject under conditions which are not the most favorable for a high degree of adaptation of attention to the reaction. In the case of long intervals with regular procedure detraction is involved, but dependent upon the ability to estimate intervals. The quickness of the reaction is varied by operating upon the subject's estimate of intervals as well as upon the degree of his attention. With the irregular procedure, however, the prolongation is due entirely to the fact that there is less adaptation of attention. Consequently, if we wish to use unfavorable intervals as a detractor, evidently we must use the irregular procedure, except in the case where no comparisons are to be made between different individuals.

To sum up, a regularly repeated 2 sec. interval gives the maximal adaptation or adjustment of attention of which the individual is capable. A given set of totally irregular intervals varying from 4 to 20 secs. constitutes a definite obstacle to the attainment of this maximal adaptation. Such a set of intervals produces prolongation of reaction time solely by its effect as a detractor from attention. We have here, then, a satisfactory method of detraction.

This method of detraction has advantages which make it far superior to any of the distractors of attention hitherto used as detractors.36 It is well known that no satisfactory distractor has yet been found.37 In any case where there is divided atten

Külpe: "It is clear that the mere employment of distracting stimuli of a certain intensity or number is absolutely no guarantee that a corresponding distraction of the attention has actually been accomplished." Outlines of Psychology, 1901, Trans. by Titchener, 429.

37 Geissler found that even the most complex combination of distractors, after a few days' work failed to induce great variations in attention. Op.

tion it is impossible to determine what proportion of attention is involved in each of the different processes. As regards other detractors, such as drugs, fatigue, etc., we have none so far as I know that can be shown to act exclusively on the process of attention, nor could we rely on such to constitute always the same amount of detracting influence. We get in many cases, undoubtedly, detraction from attention, perhaps principally that, but other detrimental effects as well, so we cannot say how much of the decrease in efficiency of the tested function is due to decrease in degree of attention and how much to an effect upon other factors than attention. Similarly with weakening the intensity of the stimulus. Intensity is undoubtedly a condition of attention, and in decreasing the intensity of the stimulus we decrease the degree of attention, other things equal, involved in its perception. But this lowered intensity of stimulus may cause prolongation of reaction time for other reasons than that of consequent lowered attention, as, for example, a longer latent period in the stimulation of the sense organ.38 While unfavorable preparatory intervals may be the best detractor hitherto employed for the purpose of measurement of attention, nothing that has been said should be interpreted as meaning that other equally good detractors may not be discovered. The writer is at present engaged in an investigation in which a quite different sort of detractor is used,-used, however, in accordance with the main principles established in the following chapters.

SUMMARY

It is necessary in reaction experiments to distinguish sharply between two principal procedures: the first, that in which the same preparatory interval is used a number of times in succession, and change from one preparatory interval to another made in regular order from the shortest to the longest; and the seccit., 513. More recently Dallenbach has come to the following conclusion: "The difficulty of obtaining a graded series of distractors is very great. In our experience, the action of the distractors is not constant, but varies from day to day, and from observer to observer." Op. cit., 507.

* Piéron, Recherches sur les lois de variation des temps de latence sensorielle en fonction des intensités excitatrices, L'Année Psychol., 1914, 17-96.

ond, that in which a number of preparatory intervals of widely different length are mixed in irregular order.

The effect of variation of the preparatory interval on reaction time, when the first procedure is used, may be summarized as follows: Intervals very near 2 secs. are the most favorable. As the interval is shortened below this most favorable region, or lengthened beyond it, the reaction time increases in a marked manner. The increase which occurs with prolongation in the preparatory interval beyond the most favorable is at first rapid, but becomes less and less marked with further increase in the duration of the interval. This increase continues to intervals over 24 secs., and is in accordance with the law, y = A + B. log x, in which y reaction time, A and B are constants, and x = the duration of the preparatory interval.

With the second procedure, that in which a number of preparatory intervals of widely different length are mixed in irregular order, little difference in reaction time occurs with the different intervals, and the reaction time obtained with each interval depends largely on the order in which the intervals are given and on the individual characteristics of the subject. A noticeable general tendency exists, however, for the longest reactions to occur with the longest and with the shortest intervals of the series, especially however with the shortest intervals, and for the shortest reactions to occur with the intervals of medium length.

An interval of about 2 secs. with the first procedure gives the shortest reaction times for any individual obtainable under any conditions. Even when the same preparatory interval is repeated a number of times in succession, maximal adaptation of attention is impossible if the interval varies much from 2 secs.

The average reaction time for the whole series, using the second procedure, of irregularly mixed and widely differing intervals, is as long as that with a very long (over 24 secs.), regularly repeated interval.

The marked prolongation in reaction time which occurs as we change from a regularly repeated preparatory interval of 2 secs. to a set of widely different irregularly mixed intervals is

due solely to the fact that in the latter case the reactions occur with less adaptation of attention to the reaction. We have, therefore, in the method of using an irregularly mixed series of widely different preparatory intervals, a method of securing less than maximal adaptation of attention, that is, a method of detraction from attention. This detraction not only acts solely on the attention, but is eminently controllable, and very uniform in its action on a given subject.

Incidentally, the data of this chapter have an important bearing on the perception of time. Since, with the regular procedure, the increase in reaction time is regular and in accordance with the same law from 2 secs. up through 24 secs., and since the increase in reaction time with this procedure is dependent upon the decrease in the absolute accuracy of the estimation of the intervals, it follows that the absolute accuracy of the estimation of intervals decreases in accordance with a law which holds without break from 2 secs. up through 24 secs. It is consequently incorrect to say of any interval less than at least 24 secs. that it is the longest which can be grasped as a single temporal perception.

THE LAW OF DETRACTION

In the last chapter I arrived at the conclusion that the use of an irregular series of widely different preparatory intervals or of regularly repeated but long preparatory intervals produced a marked prolongation of the reaction time beyond that obtained by the use of a regularly repeated 2 sec. interval; and that this prolongation was due to the lessened average degree of adaptation of attention which occurs as the result of the use of irregularly mixed or long preparatory intervals. The amount of the detraction effect produced by the irregular series of intervals is measured by the increase in reaction time beyond that obtained with a maximum adaptation of attention, that is, with a regularly repeated 2 sec. interval. Having concluded that we have here a satisfactory method of detraction from attention, I naturally took up next the investigation of the behavior of attention under detraction.

A condition could hardly be spoken of as a detractor from attention, unless, other conditions constant, it resulted in lessened efficiency in the processes to which the attention in question attached. Most writers insist that in a detraction method of some sort lies the best hope of obtaining a practical method of measuring attention, provided that suitable detractors (hitherto usually thought of as distractors) can be found. But how the decrease in efficiency, which measures the detraction effect, is to be used in measuring the degree of attention, has, it seems to me, never been worked out. It is true that some law of detraction has often been assumed or implied, though comparatively seldom stated. The implication usually has been that the better the attention the less would be the detraction produced by a stated detractor.1

1

1A good statement of a law to this effect is given by Deuchler in a footnote summing up some of the most important laws of attention. "Je groesser die