TABLE XII

(Addition and Subtraction as a Distraction)

	Single Judgment			Two Judgments			Three Judgments
Obs.	Length	Lines	Shade	Length	Lines	Shade	Length	Lines	Shade
A Number of series averaged	8	8	8	15	15	16	15	15	15
Per cent Correct Judgments	79	84	67	66	68	66	53	69	59
	\———\/———/			\———\/———/			\———\/———/
Average	77			67			60
B Number of series averaged	6	4	5	8	7	11	7	7	7
Per cent Correct Judgments	57	70	60	66	44	53	51	50	44
	\———\/———/			\———\/———/			\———\/———/
Average	62			54			52
Y Number of series averaged	8	8	7	15	16	15	14	14	14
Per cent Correct Judgments	66	60	51	56	62	56	66	57	55
	\———\/———/			\———\/———/			\———\/———/
Average	59			58			59

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.