Many of the subjects visualize a time line in the form of a curve. In
each case of this kind the introduction of a change, either in
intensity or location, if large enough to produce an effect on the
time estimation, produced a distortion on the part of the curve
corresponding to the interval affected. All of the subjects employed
in the experiments of Group 2 were distinctly conscious of the change
in attention from one point to another, as the two were stimulated
successively, and three of them, _Hy_, _Hs_ and _P_, thought of
something passing from one point to the other, the representation
being described as partly muscular and partly visual. Subjects _Mr_
and _B_ visualized the two hands, and consciously transferred the
attention from one part of the visual image to the other. Subject _Mr_
had a constant tendency to make eye movements in the direction of the
change. Subject _P_ detected these eye movements a few times, but
subject _B_ was never conscious of anything of the kind.

All of the subjects except _R_ were conscious of more or less of a
_strain_, which varied during the intervals, and was by some felt to
be largely a tension of the chest and other muscles, while others felt
it rather indefinitely as a 'strain of attention.' The characteristics
of this tension feeling were almost always different in the second
interval from those in the first, the tension being usually felt to be
more _constant_ in the second interval. In experiments of the third
group a higher degree of tension was felt in awaiting a light tap than
in awaiting a heavy one.

Evidently, in all these cases, the effect of a _difference_ between
two stimulations was to introduce certain changes in sensation
_during_ the interval which they limited, owing to the fact that the
subject expected the difference to occur. Thus in the third group of