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James R. Wilson, William W. Noyd, Akhila D. Aiyer, Anthony M. Norcia, Michael J. Mustari, Ronald G. Boothe; Asymmetric Responses in Cortical Visually Evoked Potentials to Motion Are Not Derived from Eye Movements. Invest. Ophthalmol. Vis. Sci. 1999;40(10):2435-2439.
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purpose. Normal neonates and many adults after abnormal visual development have
directional preferences for visual stimulus motions; i.e., they give
better responses for optokinetic nystagmus (OKN) and visually evoked
potentials (VEPs) in one direction than to those in the opposite
direction. The authors tested whether the VEP responses were
asymmetrical because of abnormal eye movements.
methods. VEPs were recorded from the visual cortices of five macaque monkeys:
one normal, one neonate, and three reared with
alternating monocular occlusion (AMO). They were lightly anesthetized,
followed by paralysis to prevent eye movements. They then had“
jittered” vertical grating patterns presented in their visual
fields. The steady state VEPs were analyzed with discrete Fourier
transforms to obtain the amplitudes and phases of the asymmetries.
results. The normal, control monkey had small, insignificant amplitudes of
its asymmetrical Fourier component and random phases that were not
180o out of phase across the left and right eyes. The
neonatal monkey and the AMO monkeys all had large, significant
asymmetries that were approximately 180o out of phase
between the left and right eyes.
conclusions. The neonate and abnormally reared monkeys continued to have
asymmetrical responses even after their eyes were paralyzed. Therefore,
eye movements cannot be the source of the asymmetrical amplitudes of
the VEPs, and the visual cortex is at least one source responsible for
asymmetries observed in neonates and adults reared under abnormal
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