The sun., 1901-07-07

Of recording the movsments Of the sye ant
velocity Of eye movements under norma
conditions. Prof. Dodge says:
4 For an adequate analysis OF the compiler
/, processes involved In reading 1t became
necessary not only TO know the numbei
Of the alternating periods Of moyemeni
/ and rest, but their time values as we'll The
explanation OF the general failure 70 appre-
hend the period OF eye movement either
az breau In visual perception or ~ fusion
of the field of vision. demands an accurate
knowledge Of their duration Moreover,
the problems Of the visual perception OF
Of The eye muscles. all presuppoee knowl,
edge Of the eye movement which at present
II oonsplcuously lacking
To obtain these accurate measurements,
Prof. Dodge was obliged to design a con-
siderable amount Of new apparatus. The
experimental requirements OF satisfactory
apparatus for recording eye movemens.
1. II must be capable OF operating under
normal conditions Of binocular vision.
D. II must be capable OF registering both
eyes simultaneously. s. The unit OF
measurement must be ten or lees. T.
Tho registering medium may have neither
momsntum nor inertia while the eye must
perform no extra work during registra-
ton and be subjected to no unusual con-
dltions. s. The apparatus should be made
or can be used TO record tho movements OF
q large number Of ey@. without serious
Inconvenience either during or after the
experiments. Prof. Dodge goes on to
say; -. n.,,,a. .,,..ax ,..d
satisfy all these requirements or even
a large part Of them. II 10 indeed doubt:
ful II any attachment to the eye could
be devised which would be satisfactory.
But the qualities which are demanded OF
the recording medium are possessed In
an eminent degree by Light rays and
method Of registration satisfying ne
with comparatively simple Photographic
The getsdrel plan Of the apparatus used
by Prof. Dndge was a. follows: A sensitive
aim was moved evenly In vertical plane
Immediately behind a narrow horizontal
slit in the plate hGlder Of PhotGSsTsphSlfi SsropIsSi
into such a position before the camera that
q horizontal plane bisecting the. eye through
OF the eve and passed through the horizontal
slit. n the eye were held immovable while
the sensitive nlm was exposed behind the
slit. the negative presented a series OF
at every point TO the light and dark parts
OF an imaginary line drawn horizontally
across the eye. bisecting the pupil A
horisontal movement OF the eye while the
sensitive fllm was moving behind tho slit
was marked In the negative by obliQue
lines. These oblique lines were the records
Of the eye movements and their time values
were read of from time record marked
on the sensitive film during its movement.
Photography Of the eye movements In this
simple way was open 70 some serious OBJ
jeotlons. An illumination Of the eye cap
able OF affecting the rapidly moving flm
through the small slit bad TO be rather
brilliant and even though the subjects ex-
per!enced no discomfort II was not certain
that the conditions OF vision were not dis
turbed sufficiently to affect the eye move
ments The character OF the records
also presented some serious obstacles.
The lines OF demarcatlon between the
pigmented and unpigmented portions OF the
eye were usually not sharply defined. and
although the photographs appeared fairly
distinct to the naked eye It was found I'M
possible to read them with any accuracy
when enlarged by the telescope or cathetom-
etM.
Satisfactory results were first obtained
by Prof Dodge when after many expert
ments they, hit upon a plan OF utilizing
reflector. Instead Of photogIaphing the
eye directly they photographed the move
ment OF Q bright vertical line as II was
reflected from the surface OF the cornea.
Suoh lines gave clean-out records permitting
considerable magnincation in reading.
while the amount Of light needed was COM
paratively small -...
In discussing the eyes inability to see
its own movements In mirror. Prof. Dodge
called attention to the fact that this did not
hold true absolutely. except for monocular
observation. and he suggests as tho probable
reason why In binocular observation one
occasionally perceives slight quiver,
apparently the beginning or end Of move
ment, the hypothesis that the eyes do not
move absolutely together. This hypo-
thesis seems 10 be slbstantiated by the dllfe-
ence Just remarked, between the duration
OF eve movements in different directions.
Apparently the two eyes neither start their
movements nor end them at the same In
atant