Eye movement artifact in the CNV

Abstract

During the preparatory interval between a warning click and a tone burst that signalled a lever press, a slow negative potential shift (CNV) was recorded from the scalp in ten normal adults. When the eyes were closed, involuntary eye movements during the click-tone interval consistently generated potential shifts which spread from the corneo-retinal dipole to the scalp electrodes and thereby contaminated the CNV. The CNV was quantitatively partitioned into an artifactual component caused by ocular rotation (the EAP), which summated with the second component, presumably of cerebral origin, called the “true” or tCNV. The EAP amplitudes were estimated from concurrent recordings of the electro-oculogram. In the average subject, 23% or −6.1 μV of the total CNV was comprised of EAP, and the EAP often reached from −10 to −15 μV. The accuracy of the partition was verified by comparing tCNVs recorded with eyes closed and with eyes immobilized by fixation. The CNV produced during voluntary eye movements was similarly divided into a tCNV, which was tripled in amplitude when ocular responses were made with increased speed and effort, and an EAP, which was determined solely by the amount of ocular displacement.