Lambda waves.

Lambda waves are physiological, triangular shaped, sharp transients occurring over the occipital regions when eyes are open. Lambda waves occur with saccadic eye movements during visual scanning, disappearing when eyes are closed and in sleep. They are best elicited when subjects visually scan a complex picture, therefore seen during visual exploration of a brightly illuminated object or room. The expression of these waveforms seems to be secondary to a functional activation of a common region in the brain, probably localized within parieto-occipital region.