Optical illusions of motion / by G. Stanley Hall.

  • Bowditch, H. P. (Henry Pickering), 1840-1911.
Date:
[1882]
Catalogue details

Licence: Public Domain Mark

Credit: Optical illusions of motion / by G. Stanley Hall. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    OPTICAL ILLUSIONS OF MOTION. By H. P. BOWDITCH, M.D., Professor of Pliysiologu in the Harvard iMedical School and by G. STANLEY HALL, Ph.D. Plate XVIIL In 1834, R. Ad dam described in the Philosophical Magazine the fact, often before observed, that when, after looking at a sheet of falling water, the eyes were turned toward the adjacent bank, the latter with the rocks and trees upon it seemed for a short time to move slowly upward. This was explained by Addam and also by E. Javal by assuming that the eye followed the falling mass a moment, and then slipped back, and that this oscillation was associated with the impression of motion do^vnward, but, by continuing after the eye had been turned upon a stationary object, caused us to attribute to the latter a movement in the opposite direction. This explanation is vague, was not favoured by the studies of nystagmus which it prompted, and has since been shown t9 be worthless, as M-e shall see later, by the fact that opposite motor after- effects are possible for the same retina at the same time. Analogous observations were later made by Sir David Brewster in the early days of railroad travelling^. When, e.g., after looking at objects from the window of a car we suddenly turn the eyes to the floor within, the latter seems to move away from our feet in the opposite direction. This apparent movement Helmholtz designates as dizziness (schivindeiy, and explains it by saying that when the traveller tries to fixate the objects near the train outside, his eye must be moved rapidly in a direction opposite the motion of the train. After he has become accustomed to regard the volitional impulses thus put forth as adapted to the fixation of objects, he tries, unconsciously believing his eyes to be motionless, to fixate objects at rest in the same way; thus objects on the train seem to move in the opposite sense although they arc relatively at rest. If, Helmholtz continues, instead of looking out of the car a point on the window-pane be fixated, this optical dizziness does not occur, because no motion is made by the eyeball for the fixation of PH. III. ' &oe Bri/Uh Assoeia/ion Rrportii, ISilj, 'Gl. ^ Fhij!<ioJogi.iche Optik, pp, G02-4. 21