The right column shows typical VEP signals, referred to a single subject, recorded after stimulation at increasing contrast (1, 10, 100%)

Copyright information:Taken from "Optical and electrical recording of neural activity evoked by graded contrast visual stimulus"http://www.biomedical-engineering-online.com/content/6/1/28BioMedical Engineering OnLine 2007;6():28-28.Published online 4 Jul 2007PMCID:PMC1934360. The left column contains VEPs recorded in a "without stimulus" condition: the subjects gaze at a uniform unpatterned screen. The large vertical arrows indicate the correspondence between the visual stimulation protocol and the recording duration, which lasts for 60 seconds. Each 60-second interval corresponds to the interval reported as a white/grey vertical strip in Figure 6.