Figure 1.

Experimental design and EEG responses. A,2IFC contrast discrimination task included the presentation of two consecutive stimuli. Each stimulus was presented for 100 ms and was followed by a 900 ms blank screen. Subjects were instructed to press a button to report which stimulus was of higher contrast when the fixation cross appeared. One of the two stimuli was always at base contrast (100%) and the other was of lower contrast. B, EEG recordings from single trials containing the base stimulus. Colored lines represent single trials and the black line represents the mean ERP. This example presents trials from the first stimulus interval of a single subject (electrode PO8).