TABLE XI
| Length | Lines | Shade | ||||
| Obs. | With Diffs. | Alone | With Diffs. | Alone | With Diffs. | Alone |
| A Number of series averaged | 5 | 5 | 5 | 5 | 5 | 5 |
| Per cent Correct Judgments | 98 | 96 | 96 | 96 | 98 | 94 |
| B Number of series averaged | 5 | 5 | 5 | 5 | 5 | 5 |
| Per cent Correct Judgments | 90 | 92 | 96 | 94 | 78 | 84 |
| Y Number of series averaged | 7 | 8 | 8 | 8 | 7 | 8 |
| Per cent Correct Judgments | 73 | 76 | 75 | 64 | 88 | 67 |
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.