As soon as I had reached this first experimental result, I began to see how it might harmonize with known psychological facts.  Some years ago a Hungarian psychologist[37] showed by interesting experiments that if a series of figures is exposed to the eye for a short fraction of a second, equal digits are seen only once, and he came to the conclusion that equal impressions in such a series inhibit each other.  In the Harvard laboratory we varied these experiments by eliminating the spatial separation of those numbers.  In our experiments the digits did not stand side by side, but followed one another very quickly in the same place.[38] Similar experiments we made with colors and so on.  Here, too, we found that quickly succeeding equal or very similar impressions have a tendency to inhibit each other or to fuse with each other.  Where such an inhibition occurs, we probably ought to suppose that the perception of the first impression exhausts the psychical disposition for this particular mental experience.  The psychophysical apparatus becomes for a moment unable to arouse the same impression once more.

The above described new experiments suggest to me that this inhibition of equal or similar impressions is found unequally developed in different individuals.  They possess a different tendency to temporary exhaustion of psychophysical dispositions.  There are evidently persons who after they have received an impression are unable immediately to seize the same impression again.  Their attention and their whole inner attitude fails.  But there are evidently other persons for whom, on the contrary, the experience of an impression is a kind of inner preparation for arousing the same or a similar impression.  In their case the psychophysical dispositions become stimulated and excited, and therefore favor the repetition.  If, as in our experiments, the task is simply to judge the existence of equal or similar impressions without any strain of attention, the one group of persons must underestimate the number of the equal impressions because many words are simply inhibited in their minds and remain neglected, the other groups of persons must from their mental dispositions overestimate the number of similar words.  From here we have to take one step more.  If these two groups of persons have to perform a task in which it is necessary that not a single member of a series of repetitions be overlooked, it is clear that the two groups must react in a very different way.  Now a perfect perception of every single member is forced on them.  Those who grasp equal impressions easily, and who are prepared beforehand for every new repetition by their inner dispositions, will follow the series without strain and will experience the repetition itself with true satisfaction.  On the other hand, those in whom every impression inhibits the readiness to receive a repetition, and whose inner energy for the same experience is exhausted, must feel it as a painful and fatiguing effort if they