Human cortical magnification factor and its relation to visual acuity
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The magnification factor (M) of the retina is the linear extent of visual striate cortex to which each degree of the retina projects. It has been suggested that magnification factor is directly proportional to visual acuity, but magnification factor measured in monkeys was compared with visual acuity in man. Here we first describe calculation of the magnification factor in man, and then compare it to human visual acuity.
We calculated M for the first 30 degrees of the lower visual field by using infor mation provided by Brindley and Lewin (1968), who plotted the distribution of phosphenes evoked by stimulation of visual cortex in a human patient with electrodes implanted on the visual cortex. Since the inter-electrode distance was specified it was possible to calculate M for each of many pairs of electrodes by measuring the angular separation and mean eccentricity of the corresponding pairs of phosphenes. For the lower visual field, M was approximately 4 mm/degree at 2 degrees eccentricity and declined monotonically to 0.5 mm/degree at 25 degrees eccentricity.
The results indicated that the reciprocal of M is directly proportional to the minimum angle of resolution and, correspondingly, that the magnification factor is directly proportional to visual acuity in man.
By extrapolating this function for the whole of the visual field it was possible to estimate the area of striate cortex. The total extent of striate cortex estimated in this way agreed closely with previous direct measurements, suggesting that the measurements of M are accurate.
- Brindley, G.S., Donaldson, P.E.K., Falconer, M.A., Rushton, D.N.: The extent of the region of the occipital cortex that when stimulated gives phosphenes fixed in the visual field. J. Physiol. (Lond.) 225, 57–58 (1972)
- Brindley, G.S., Lewin, W.S.: The sensations produced by electrical stimulation of the visual cortex. J. Physiol. (Lond.) 196, 479–493 (1968)
- Cowey, A.: Projection of the retina onto striate and prestriate cortex in the squirrel monkey, Saimiri sciureus. J. Neurophysiol. 27, 366–393 (1964)
- Cowey, A., Rolls, E.T.: Cortical magnification factor in man and its relation to visual acuity. Brain Res. (in press)
- Cragg, B. G., Ainsworth, A.: The topography of the afferent projections in circumstriate visual cortex of the monkey studied by the Nauta method. Vision Res. 9, 733–747 (1969)
- Daniel, P. M., Whitteridge, D.: The representation of the visual field on the cerebral cortex in monkeys. J. Physiol. (Lond.) 159, 203–221 (1961)
- Filimonoff, I.N.: Über die Variabilität der Grosshirnrindenstruktur. II. Regio occipitalis beim erwachsenen Menschen. J. Psychol. Neurol. (Lpz.) 44, 1–96 (1932)
- Holmes, G.: Disturbances of vision by cerebral lesions. Brit. J. Ophthal. 2, 353–384 (1918)
- Polyak, S.: The vertebrate visual system. University of Chicago Press 1957
- Rolls, E.T., Cowey, A.: Topography of the retina and striate cortex and its relationship to visual acuity in rhesus monkeys and squirrel monkeys. Exp. Brain Res. 10, 298–310 (1970)
- Sholl, D.A.: The organization of the cerebral cortex. London: Methuen 1956
- Wertheim, T.: Über die indirekte Sehschärfe. Z. Psychol. Physiol. Sinnesorg. 7, 172–189 (1894)
- Weymouth, F.W.: Visual sensory units and the minimal angle of resolution. Amer. J. Ophthal. 46, 102–113 (1958)
- Zeki, S.M.: Representation of central visual field in prestriate cortex of monkey. Brain Res. 14, 271–291 (1969)
- Human cortical magnification factor and its relation to visual acuity
Experimental Brain Research
Volume 21, Issue 5 , pp 447-454
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