Vision and work / by Freeland Fergus.

  • Fergus, A. Freeland (Andrew Freeland), 1858-1932
Date:
1907
Catalogue details

Licence: In copyright

Credit: Vision and work / by Freeland Fergus. 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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    ception of movement. Thus, if a person with a healthy eye look straight in front of him, and hold up his right hand so that the angle between the line of vision and the line joining the fingers of the hand with the eye is approximately 90°, and if the fingers of the hand be made to move, the person is at once conscious of the slightest movement; not only so, but by his light sense and by his power of distinguishing movement, he is able to locate the object perfectly well in space, at any rate so far as its alignment is concerned. Thus, we see that for the work of a labourer visual acuteness is not required, but only this sense of alignment which depends upon those stimulations of the retina which are more par- ticularly associated with the light sense. One other observation falls to be made. The sense of align- ment is all that is required for the employment of the larger tools. Again and again I have found persons who are possessed of only one eye quite able to use a hammer, or to wheel a barrow, or to handle a spade, or pick, or shovel, and any one who tries it will find that he experiences no difficulty whatever in performing any of these manipulations with one eye shut. The reason of this is perfectly obvious; in all these forms of labouring the important matter is not the relative distances of various objects to each other, but it is the alignment, and the absolute distance of the object from the person who is engaged in the work. One other remark may be made in conclusion. In an earlier part of this communication it was stated that the visual acuteness is a function of that part of the retina which is known as the macula lutea. There are good grounds for believing that it is also a function of certain definite centres in the cerebral cortex. If a young child, say between the ages of 1 and 3, begins to squint with one eye, then if that squint is allowed to remain for any length of time, the visual acuteness undergoes serious and per- manent deterioration; probably it does so within a period of two months from the onset of the squint. Now, if later in life the eye becomes straight it is found that good visual acuteness, as tested by Snellen's scale, is not regained, the visual acuteness may improve a little, but only very slightly, although the patient will have that perception of form which depends upon the light sense. The explanation of this circumstance, which seems most probably true, is, that in the early years of life the cerebral cortex becomes differentiated according to the function which it is afterwards to subserve. From the squinting eye no stimuli suitable
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