A physician's notes on ophthalmology. 2nd series / by J. Hughlings Jackson.

  • Jackson, John Hughlings, 1834-1911.
Date:
[1875]
Catalogue details

Licence: Public Domain Mark

Credit: A physician's notes on ophthalmology. 2nd series / by J. Hughlings Jackson. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Whatever number of motions we may be able to interpolate, and whether they be real or imaginary, we shall still find, at the end of the series, a motion antecedent, and a colour con- sequent.”— (Mill’s Logic, vol ii, p. 436.) THE ANATOMICAL SUBSTRATA OF VISUAL IDEAS. Dr. Hughlings Jackson has long taught that the convolutions, like the inferior nervous centres, represent impressions and move- ments. In other words, he believes that the unit of composition of the nervous system from the lowest to the highest centres is a sensori-motor arrangement. He thinks it to be clearly so in' the case of the substrata of visual ideas. He urges that, in actually seeing, there is concerned a retinal impression and an ocular movement; in thinking of (ideal seeing) an object there is concerned a nervous arrangement which represents these two elements, the motor as necessarily as the sensory. There are three qualities in bodies: secondary or dynamical, primary or statical, and secundo-primary or statico-dynamical. The secondary or dynamical properties are estimated by sensory nerves and centres; the primary or statical are estimated by motor nerves and centres. Dr. Hughlings Jackson supposes the secundo-primary or statico-dynamical properties to be esti- mated by impressions and movements represented in the cere- bellum ; of these, nothing is said in this note (see p. 23). The colour of an object is, on its physiological and ana- tomical side, simply an affair of the retina and other higher sensory centres therewith associated ; on the other hand, its size and shape are estimated by ocular movements.* So far for acquiring visual ideas of objects for actually seeing them. But when we have seen an object we can see it again ideally, or, in synonymous terms, “think of it.” Dr. Hughlings Jackson believes (in accordance with the opinions of Spencer and Bain) that the ideal seeing is a repetition of the actual seeing, with a difference corresponding to the difference that one is a faint mental state, the other a vivid mental state. In thinking of objects the central discharge is (1) sight, and (2) limited to the centre. In actually seeing them it is (1) strong, and (2) spreads from periphery to the centre and from centre to periphery. In short, he believes that the anatomical substratum of the idea of an object consists of two .elements, a sensory and a motor. Speaking of visual ideas, the substratum represents a particular retinal impression and also a particular ocular move- ment. * It is understood, of course, that the estimation by the eye is symbo- lical. On the association of ocular movements with tactual movements, as evidenced by cases of hemiplegia with lateral deviation of the eyeballs, see last Periscope, p. 97. The association of hemiopia with hemi-aneesthesia is similarly significant (see last Periscope, p. 101, and note in this Periscope on Autopsy in a case of Hemiopia with Hemiplegia and Hemi-aneesthesia).
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