Notwithstanding the precautions taken to secure the full energy of attention for the single judgment process, as already indicated in the discussion preliminary to these experiments,—namely, by making the stimulation conditions so near the threshold that only a part of the judgments could be given correctly,—there still appeared a probability that there was free energy of attention during the single judgment process. The observers seemed to do more work when more judgments were asked for. If this is true, the results of Table X are not a true index of interference. If there is free energy during the moment of making the single judgment, this may readily be used for another process when combined with the first, and so there will be no interference. This is a sufficient proof so far as it has immediate bearing upon the interval discrimination experiment, but the further question as to what will take place if we can use this free energy, if it exists, in both processes alike, is an important one for the question of the relation of two processes going on together in consciousness.

To ascertain the fact in this matter, I performed a series of experiments with the same observers, in which previous occupation of the mind served as a distraction. The distraction consisted in a simple arithmetical operation,—addition or subtraction. The moment before giving the stimulus for the judgment processes,—in the place of the "ready" signal, I would call out some numbers, as, for example, "twenty-four from sixty-three" or "fifty-seven and fifteen," the first indicating subtraction and the second addition. The answer to the addition or subtraction was always given before the judgment or judgments, to make sure that it was performed. And in any case where the observer knew that the addition or subtraction was done before he attended to the stimulus for the judgment, that particular test was thrown out. The results are given in the same form as in Table X.

TABLE XII

(Addition and Subtraction as a Distraction)

Single JudgmentTwo JudgmentsThree Judgments
Obs.LengthLinesShadeLengthLinesShadeLengthLinesShade
A Number of
series averaged		888151516151515
Per cent Correct
Judgments		798467666866536959
\———\/———/\———\/———/\———\/———/
Average776760
B Number of
series averaged		6458711777
Per cent Correct
Judgments		577060664453515044
\———\/———/\———\/———/\———\/———/
Average625452
Y Number of
series averaged		887151615141414
Per cent Correct
Judgments		666051566256665755
\———\/———/\———\/———/\———\/———/
Average595859

These results (general average percentages) show, for observer A, a more regular and somewhat larger falling-off with combination than in Table X, for B and for Y, a diminished falling-off, and relatively less for the three than for the two combined judgments. The percentages are lower throughout. This is a result to be expected. But there is no notable change in the relative lowering of two judgments in comparison with single judgments, or of three in comparison with two, such as should appear if, as supposed, in the experiment resulting in Table X, there had been free energy of attention in the case of the single judgment.

It was my aim in these experiments, with distraction through another simultaneous process, to secure a uniform residue of attention for the judgment processes, whether single, in twos, or in threes. The arithmetical operations were therefore as uniform as possible. But it may readily be that very unequal demands were made upon a given observer by successive operations, one's automatisations in number-work may be so various. These would no doubt tend to average up in the course of the whole work running through several weeks. But in order to make more sure of the point, I tried another means of using the free energy of attention which may exist in the case of the single judgment, namely, by suggesting a judgment or series of judgments just before an exposure. It will be recalled that the order of judgments was always the same as that of the tables, and that all were expressed as minus, plus, or equal. So if the experimenter called out before a three-judgment exposure, "plus, equal, minus," it would be in the nature of a challenge to the observer to assure himself beyond a doubt whether or not the exposure showed the left-hand rectangle as longer than the right, having the same number of lines, and being less bright. The so-called suggestion was a distinct factor in heightening attention. This is shown especially in Y's case by the larger percentage of correct judgments. Results are averaged in Table XIII.

TABLE XIII

(Attention heightened by Suggested Judgments)

Single JudgmentsTwo JudgmentsThree Judgments
Obs.LengthLinesShadeLengthLinesShadeLengthLinesShade
A Number of
series averaged		242677888
Per cent Correct
Judgments		908985878176927277
\———\/———/\———\/———/\———\/———/
Average878180
B Number of
series averaged		434897888
Per cent Correct
Judgments		857092848083847481
\———\/———/\———\/———/\———\/———/
Average828280
Y Number of
series averaged		665111312161616
Per cent Correct
Judgments		887594908177897470
\———\/———/\———\/———/\———\/———/
Average868378