On binocular flicker and the correlation of activity of 'corresponding' retinal points / by C. S. Sherrington.

  • Charles Scott Sherrington
Date:
[1904]
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Licence: In copyright

Credit: On binocular flicker and the correlation of activity of 'corresponding' retinal points / by C. S. Sherrington. Source: Wellcome Collection.

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

    11/39 (page 32)
    wire candle-shaped lamp of considerable, i.e. 12 cm., length, and fixing it accurately in the axis of the cylindrical screen. The rotating screen was blackened inside to minimise reflection. That the brightness of illumination of the four holes was really equal was ascertained at outset of each series of observations by finding the rate of revolution of the circular shutter required just to extinguish flicker at each of the four holes. If the rate of revolution was the same for all, the equalisation of the lighting of the four holes was considered to have been attained. In a number of observations made before the arrangement of the apparatus took its final form, a single haploscopic image was presented to the visual field. The right and left components of this image could be either synchronously or alternately presented, according to the dis- position of the apparatus, and it was easy to change the composition of the haploscopic image from one form to the other. But to effect the change demanded a break of at least 5 seconds, and usually involved some disturbance of the observer by noise. This successive method of comparison was at a disadvantage on these accounts; it suffered in facility and precision. The measurements it yielded were however broadly similar to those obtained by the method of more immediately successive comparison adopted finally. In the latter, the apparatus for which is described in the small print above, two haploscopic images, one close above the other, were placed in the central field. The right and left components of each of these could be either synchronously or alternately compounded in each. The foveal gaze could be turned from one to the other of them when and as often as the observer desired, and in the fraction of a second by a slight, i.e. less than 3, movement of the eyeballs. The comparison thus instituted was much more facile and sure. The two images concurrently presented were so near together that it was easily possible while fixating the narrow dark interval between them to observe both and watch for appearance or disappearance of flicker in either. But the sensitiveness of even the median (central) region of the visual field is not everywhere the same as tested by perception of flicker. It was preferable to keep fixating the two images alternately, first one, then the other, and thus to watch for the earliest appearance (or disappearance) of flicker in either, using for each the macular retina itself. An image would fail to flicker when received on the fovea that would distinctly flicker when its image fell just outside the fovea. Thus the disc image that just did not perceptibly flicker when its