field, that is, with the perception of the mutual
relations as to direction and distance, of objects
which are viewed simultaneously.... Undoubtedly,
however, sensations of eye-movements, and of head-and
body-movements as well, afford us a scale for measuring
the displacements which our entire visual field and
every point in it undergo within the surrounding totality
, which we conceive of as fixed.
We estimate according to the length of such movements,
or at least we deduce therefrom, the distance through
fixed space which our view by virtue of these movements
has traversed.... They themselves are nothing
for our consciousness but a series of purely intensive
states. But in experience they can come to indicate
distance traversed.” Now in turning the
eye from a luminous object, O
, to some other
, the distance as simply contemplated
is more or less subdivided or filled in by the objects
which are seen to lie between O
or if no such objects are visible the distance is
still felt to consist of an infinity of points; whereas
the muscular innervation which is to carry the eye
over this very distance is an undivided unit.
But it is this which gives us our estimate of the arc
we move through, and being thus uninterrupted it will
appear shorter than the contemplated, much subdivided
, just as a continuous line appears
shorter than a broken line. “After such
analogies, now, the movement of the eye from O
, that is, the arc which I traverse, must
be underestimated” (ibid.
, S. 67).
There is thus a discrepancy between our two estimates
of the distance OP
. This discrepancy is
felt during the movement, and can be harmonized only
if we seem to see the two fixation-points move apart,
until the arc between them, in terms of innervation-feeling,
feels equal to the distance OP
in terms of
its visual subdivisions. Now either O
can both seem to move apart from each other,
or else one can seem fixed while the other moves.
But the eye has for its goal P
, which ought
therefore to have a definite position. “P
appears fixed because, as goal, I hold it fast in
my thought” (loc. citat.
). It must
, therefore, which appears to move; that
must dart backward as the eye moves forward
. Thus Lipps explains the illusion.
 Lipps, Th., Zeitschrift
f. Psychologie u. Physiologie der
Sinnesorgane, 1890, I., S. 60-74.
Such an explanation involves many doubtful presuppositions,
but if we were to grant to Lipps those, the following
consideration would invalidate his account. Whether
the feeling of innervation which he speaks of as being
the underestimated factor is supposed to be a true
innervation-feeling in the narrower sense, or a muscular
sensation remembered from past movements, it would
in the course of experience certainly come to be so