In discussing the function of visual acuity one is inclined to speak at times too casually of perception of light, of color vision and of perception and identification of form. One may fail, however, except when under the necessity of considering details of retinal physiology, to differentiate retinal function into that which is purely ocular and that which is neurocentral, even of a subcortical nature. Thus, one is vague and indecisive in separating retinal sensitivity and response into certain stages : the first, that of primitive perception ; the second, that wherein there is an integration of recepts of a more highly discriminative pattern in which qualitative as well as quantitative details of the constituent sensations carry into consciousness factors such as attention and awareness, the third, a "learning by experience" stage.
The first stage can be called a dyscritic stage; it is a purely primitive one wherein no discrimination or
SPAETH EB. CLINICAL DETERMINATION OF THE LIGHT THRESHOLD. Arch Ophthalmol. 1934;11(3):462–485. doi:10.1001/archopht.1934.00830100084005
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