Harvard Psychological Studies, Volume 1 | Page 7

slight. Inasmuch as the
'false' streak is often one third as long as the distance moved through, a
movement of rebound, such as Cornelius means, would have to be one
third of the arc intended, and could therefore easily have been noticed.
Furthermore, the researches of Lamansky,[12] Guillery,[13] Huey,[14]
Dodge and Cline,[15] which are particularly concerned with the
movements of the eyes, make no mention of such rebounds.
Schwarz[16] above all has made careful investigations on this very
point, in which a screen was so placed between the observer and the
luminous spot that it intervened between the pupil and the light, just
before the end of the movement. Thus the retina was not stimulated
during the latter part of its movement, just when Cornelius assumed the

rebound to take place. This arrangement, however, did not in the least
modify the appearance of the false streak.
[12] Lamansky, S., Pflüger's Archiv f. d. gesammte Physiologie, 1869,
II., S. 418.
[13] Guillery, ibid., 1898, LXXI., S. 607; and 1898, LXXIII., S. 87.
[14] Huey, Edmund B., American Journal of Psychology, 1900, XI., p.
283.
[15] Dodge, Raymond, and Cline, T.S., PSYCHOLOGICAL REVIEW,
1901, VIII., PP. 145-157.
[16] Schwarz, Otto, Zeitschrift J. Psychologie u. Physiologie der
Sinnesorgane, 1892, III., S. 398-404.
This work of Schwarz certainly proves that the explanation of
Cornelius is not correct. Schwarz found that the phenomenon takes
place as well when the head moves and the eyes are fixed relatively to
the head, as when the eyes alone move. He furthermore made this
observation. Meaning by a the point of departure and by b the goal of
either the eye-or the head-movement, movement, he says (ibid., S.
400-2): "While oftentimes the streak of the after-image extended
uninterruptedly to the point b, or better seemed to proceed from this
point,--as Lipps also reported--yet generally, under the experimental
conditions which I have indicated, two streaks could be seen, separated
by a dark space between; firstly the anomalous one" (the false streak)
"rather brilliant, and secondly a fainter one of about equal or perhaps
greater length, which began at the new fixation-point b and was
manifestly an after-image correctly localized with regard to the
situation of this point. This last after-image streak did not always
appear; but it appeared regularly if the light at a was bright enough and
the background dark.... It was impossible for this second after-image
streak to originate in the point b, because it appeared equally when b
was only an imaginary fixation-point.... This consideration makes it
already conceivable that the two parts of the total after-image are two
manifestations of the one identical retinal stimulation, which are

differently localized.... Therefore we must probably picture to ourselves
that the sensation from the strip of the retina stimulated during the
quick eye-movement is, during the interval of movement or at least
during the greater part of it, localized as if the axis of vision were still
directed toward the original fixation-point. And when the new position
of rest is reached and the disturbance on the retinal strip has not
wholly died away, then the strip comes once more into consciousness,
but this time correctly localized with reference to the new position of
the axis of vision. By attending closely to the behavior as regards time
of both after-image streaks, I can generally see the normal after-image
develop a moment later than the anomalous one" (that is, the false
streak). Schwarz finally suggests (S. 404) that probably between the
first and second appearances of the streak an 'innervation-feeling'
intervenes which affords the basis for localizing the second streak
('correctly') with reference to the new position of the eye.
After this digression we return to consider how this phenomenon is
related to the hypothesis of anæsthesia during eye-movements. If we
accept the interpretation of Schwarz, there is one retinal process which
is perceived as two luminous streaks in space, localized differently and
referred to different moments of time. It is surprising, then, that a
continuous retinal process is subjectively interpreted as two quite
different objects, that is, as something discontinuous. Where does the
factor of discontinuity come in? If we suppose the retinal disturbance to
produce a continuous sensation in consciousness, we should expect,
according to every analogy, that this sensation would be referred to one
continuously existing object. And if this object is to be localized in two
places successively, we should expect it to appear to move
continuously through all intervening positions. Such an interpretation is
all the more to be expected, since, as the strobic phenomena show, even
discontinuous retinal processes tend to be interpreted as continuously
existing objects.
On the other hand, if there were a central anæsthesia during
eye-movement, the continuous process in the retina could not produce a
continuous sensation, and if the interval were long