Illustrations of paradigm.

Sequences in which stimuli are presented centrally. Deviant (orange) and control (purple) stimuli have the same probability (16.67%) of occurring in their respective sequences. At least three standard (green) stimuli separate deviants and each stimulus appears for 100 ms. A. Orientation oddball sequence in which the orientation of the deviant was 95° and the orientation of the standard was 128°. The standard and deviant values alternate across orientation blocks. B. Orientation control sequence in which the orientation of each stimulus is as follows: 84°… 117° … 139° … 106° … 128° … 95°… (… denotes the 400 ms ISI that is not shown). The Michelson contrast of all Gabor patches was .393 in all orientation blocks. C. Contrast oddball sequence in which the Michelson contrast of the deviant was always .393 and the Michelson contrast of the standard was always .846. D. Contrast control sequence in which the Michelson contrast of each stimulus is as follows: .544 … .997 … .695 … .242 … .846 … .363. The orientation of all Gabor patches within a contrast block was either 95° (as illustrated) or 128°. E. Magnified fixation cross during a target (bottom) and non-target (top) trial in a contrast block in which the Gabor patch Michelson contrast was .544 and the orientation was 95°.