less
pronounced jerks, for the final number. Thus I would often respond with
4 instead of 8, or 3 instead of 9, or with 3 when the problem was 3+2,
just as Hans had so often done. In these tests, too, the difficulty of
getting the number 1, as well as the larger numbers, came to light. Thus
three times in succession 17 was indicated as 4, as 9, and as 17. But
after some practice I was able to give numbers as high as 58 and 96. The
frequency of the errors of one unit too many and of one unit too few is
also noticeable in these tests.

We also found desirable corroboration, by trustworthy subjects, of the
introspective observations of the author, which were reported in Chapter
III, with regard to the significance of concentration and the curve of
attention. It is hardly necessary to mention that no attempts were made
to influence the subjects in their accounts by asking suggestive
questions. The most valuable feature about these tests was that the mute
horse had now been replaced, as it were, by an animal capable of speech,
and that it was now possible to follow the same process both from within
and from without. Two illustrations may be welcome. The one who took the
part of the horse gave three taps and made the following entry: "At 3 I
saw a slight upward jerk of the head on the part of the questioner". The
questioner however had thought of 4, and made the following note,
without knowledge of the other's entry: "I was aware of extreme tension,
so that it was impossible for me to get beyond 3". Or again, the
'horse', reacting to a movement on the part of the questioner, stopped
at 3, but the latter, having intended to obtain 2, made the following
entry: "I noted clearly that I ceased thinking of the number too late,
and did not put on the brakes, as it were, until I had arrived at 3". We
see that errors here were entirely the fault of the questioner, just as
had been the case in the tests with Hans. (See page 151f.).

In a second group of experiments I asked a subject to fix his mind upon
certain concepts, such as "up", or "down", "right" or "left", "yes" or
"no", and others, in any order he pleased, but with the greatest
possible degree of concentration. The subject each time had the choice
of four or six concepts, and he was told to think of one of them at the
signal "Now!". How he was to 'think' the concept was left entirely to
him. He was also told to interpolate the series with a 'blank', that is,
to think of noth