devised a very ingenious attachment for a perimeter 'to determine just
what is seen during the eye-movement.'[18] The eye was made to move
through a known arc, and during its movement to pass by a very narrow
slit. Behind this slit was an illuminated field which stimulated the
retina. And since only during its movement was the pupil opposite the
slit, so only during the movement could the stimulation be given. In
the first experiments nothing at all of the illuminated field was
seen, and Dodge admits (_ibid._, p. 461) that this fact 'is certainly
suggestive of a central explanation for the absence of bands of fusion
under ordinary conditions.' But "these failures suggested an increase
of the illumination of the field of exposure.... Under these
conditions a long band of light was immediately evident at each
movement of the eye." This and similar observations were believed 'to
show experimentally that when a complex field of vision is perceived
during eye-movement it is seen fused' (p. 462).

[18] Dodge, PSYCHOLOGICAL REVIEW, 1900, VII., p. 459.

Between the 'failures' and the cases when a band of light was seen, no
change in the conditions had been introduced except 'an increase of
the illumination.' Suppose now this change made just the difference
between a stimulation which left _no_ appreciable _after-image_, and
one which left _a distinct one_. And is it even possible, in view of
the extreme rapidity of eye-movements, that a retinal stimulation of
any considerable intensity should not endure after the movement, to be
_then_ perceived, whether or not it had been first 'perceived during
the movement'?

Both of Dodge's experiments are open to the same objection. They do
not admit of distinguishing between consciousness of a retinal process