It is not possible to ascertain to how great an extent subject _Sh_
inhibited the more external sensations, but certainly if he succeeded
to an unusual degree in so doing, that fact would explain the absence
of effect of stimulation difference in his case.

Explanation has still to be offered for the variable effect of
intensity difference upon the _second_ interval. According to all
subjects except _Sn_, there is a radical difference in attitude in the
two intervals. In the first interval the subject is merely observant,
but in the second he is more or less reproductive. That is, he
measures off a length which seems equal to the standard, and if the
stimulation does not come at that point he is prepared to judge the
interval as 'longer,' even before the third stimulation is given. In
cases, then, where the judgment with equal intensities would be
'longer,' we might expect that the actual strengthening or weakening
of the final tap would make no difference, and that it would make very
little difference in other cases. But even here the expectation of the
intensity is an important factor in determining tension changes,
although naturally much less so than in the first interval. So we
should still expect the lengthening of the second interval.

We must remember, however, that, as we noticed in discussing the
experiments of Group 2, there is complicated with the lengthening
effect of a change the _bare constant error_, which appears even when
the three stimulations are similar in all respects except temporal
location. Compare _WWW_ with _SSS_, and we find that with all five
subjects the constant error is decidedly changed, being even reversed
in direction with three of the subjects.

Now, what determines the direction of the constant error, where there