TABLE VIII
| Obs. | Sing. Tact | Sing. Vis. | Tact. and Vis. | Two Tact. | Two Vis. | Two Tact. and Two Vis. |
| A Number of series averaged | 6 | 6 | 6 | 6 | 6 | 6 |
| Per cent Correct Judgments | 87 | 88 | 83 | 9 | 81 | 83 |
The next additional combination was a pair of judgments based upon auditory stimuli. Four electric clickers were placed on the wall behind the observer. Two were loud and two faint. Each pair was accurately adjusted so they were of the same intensity and quality. One of each pair, i. e., one loud and one faint, were hung about four feet to the left of the observer's median plane. The other two were hung at an equal distance to the right of this plane. The circuit making the click was made by a switch closed by the pendulum as it fell. The experimenter by pressing any one of four buttons gave the one of the clicks he desired. The observer's two judgments were as to the loudness and the position of the click.
TABLE IX
| Six Judgments Together | ||||||||||||
| Two Vis. | Two Tact. | Two Aud. | Visual | Tactual | Auditory | |||||||
| Obs. | Lgth. | Pos. | Num. | Pos. | Inten. | Pos. | Lgth. | Pos. | Num. | Pos. | Inten. | Pos. |
| B Number of series averaged | 8 | 8 | 8 | 8 | 8 | 8 | 14 | 14 | 14 | 14 | 14 | 14 |
| Per cent Correct | 82 | 94 | 89 | 100 | 94 | 92 | 89 | 97 | 86 | 96 | 70 | 86 |
| Judgments | \——————————⌄——————————/ | \——————————⌄——————————/ | ||||||||||
| Average | 91.7 | 87.3 | ||||||||||
| Bo Number of series averaged | 12 | 12 | 12 | 12 | 12 | 12 | 20 | 20 | 20 | 20 | 20 | 20 |
| Per cent Correct | 77 | 91 | 87 | 97 | 81 | 82 | 77 | 93 | 85 | 98 | 81 | 80 |
| Judgments | \——————————⌄——————————/ | \——————————⌄——————————/ | ||||||||||
| Average | 85.8 | 85.7 | ||||||||||
It is evident, on the face of these returns, that there is no positive assurance of interference. Each of these observers had been in some part of the complication work. And so the inference from lack of evidence here can be carried back to that work, and we may rest assured that the lack of accuracy in interval discrimination work by these observers was due in minimal measure, if in any, to interference of the mental processes, auditory and visual, tending to proceed at the same time. Some parts of the results here presented look like evidence for interference. But there is, on the whole, just as much evidence of what one might call facilitation, in combination, as there is of interference.
There is one source of possible explanation for the non-appearance of evidence of interference in these results: that is the fact that the stimuli are disparate, and so probably take different times for maturing. Thus the judgment processes, so far as they thus start from disparate sensations, may start at different times. There was good reason for using disparate stimuli first for the combination of two mental processes, as this was the closest related to the simple interval discrimination experiment to which the complication experiment had been reduced. But this objection is now easily overridden by making the conditions of experiment such that all judgments start from one and the same perceptual process.
ONE, TWO, AND THREE JUDGMENTS BASED UPON A SINGLE SENSE-PERCEPTION
The conditions here were such that the perceptual basis for any one of the single judgments was at the same time the possible basis for any other single judgment and also for any or all of them combined. What judgment or judgments were given depended entirely upon the directions given, and the consequent preparation of the attention. Under these conditions, there could no longer be any doubt about the even start of all judgments, so far as outer conditions were concerned. The only remaining cause of an uneven finish—lagging of a process, as shown by its increased inaccuracy when combined—must be interference with its progress by other processes going on at the same time.