NEURAL NOISE LIMITATIONS ON INFANT VISUAL SENSITIVITY

Visual contrast sensitivity is poor in newborn human infants, but impr oves rapidly to approach adult levels by 8 months of age(1-5). During this period, infant sensitivity can be limited by physical factors aff ecting photon capture, such as eye size and photoreceptor density(6,7) . Here we show that infant visual sensitivity is also limited by high levels of noise in the neural transduction process. Using a non-invasi ve electrophysiological measurements(8-10) and a visual noise titratio n technique(11), we have found that intrinsic neural noise in neonates is approximately nine times higher than in adults. As intrinsic neura l noise decreases during infancy, contrast sensitivity improves propor tionally, suggesting that neural noise places critical limits on contr ast sensitivity throughout development. Moreover, contrast gain contro l(12), an inhibitory process that adjusts visual responses to changing stimulation, is in place and operating in infants as young as 6 weeks of age, in spite of high levels of neural noise and significant immat urities in contrast sensitivity, The contrast gain control that we obs erved in human neonates may serve as a building block for more complex forms of visual inhibition, which develop later in infancy(13).