The rotated-heads oddball paradigm (Begleiter et al., 1984) used in the current study is a complex visuospatial task which has been repeatedly shown to differentiate externalizing subjects and non-externalizing controls (Iacono et al., 2002; Polich et al., 1994). Stimuli consisted of four infrequently occurring target stimuli (n = 80) interspersed with one frequently occurring non-target stimulus (n = 160) presented in pseudo-random order. Target stimuli resembling “heads” were presented as an oval with one triangular “nose” appearing on either the top (oriented up) or bottom (oriented down) of the oval and one “ear” appearing on either the left or right side of the same oval. The non-target stimulus was a simple oval of the same size and shape without nose or ear. Sitting in a sound-attenuated dimly-lit room, subjects were instructed to press a button on the left or right armrest of a chair (indicating which side of the stimulus “head” the “ear” appears on) to target stimuli and ignore non-target stimuli. For half of target stimuli, the head was oriented towards the top of the screen (response-hand is congruent
