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The discharges of single neurones in the parvocellular and magnocellular laminae of the macaque's lateral geniculate nucleus (l.g.n.) were recorded with glass-insulated tungsten micro-electrodes. Linearity of spatial summation was examined using the test devised by Hochstein magnocellular units to stimuli modulated at frequencies nearer 20 Hz. The loss of sensitivity as temporal frequency fell below optimum was more marked in magnocellular than parvocellular units. Changes in temporal frequency altered the shapes of the spatial contrast sensitivity curves of both parvocellular and magnocellular units. These changes could be explained by supposing that centre and surround have different temporal properties, and that the surround is relatively less sensitive to higher temporal frequencies.
Derrington et al. (Sat,) studied this question.