The origin of the initial negative component of the averaged lambda potential recorded from midline electrodes

There are differences in morphology and latency between averaged lambda waves and averaged pattern reversal visual evoked potentials (VEPs). Averaging of lambda potentials recorded from Oz-Fz, Oz-Cz and Oz-Pz was synchronised from various points in the electro-oculogram (EOG) wave form, during targeted saccadic eye movements across a checkerboard which was subsequently used for pattern reversal VEPs. EOG and blinks (electrical and infra-red) were recorded and also averaged from eye movements performed in darkness. The initial, prominent, negative component in the averaged lambda wave was shown to be due to eye blink artefact caused by a partial lowering of the upper lid, each blink coinciding with every saccadic eye movement which elicited a lambda wave when scanning the pattern but not when the eye moved in darkness.