Researchers also have found supporting evidence for the frontal system model from studies in which alcoholics and nonalcoholics were asked to perform tests known to reveal deficits caused by lesions in frontal brain systems in animals (Oscar-Berman et al. 1992). One such task used with nonhuman primates with frontal brain lesions is the delayed-response (DR) task in which a reward is placed into a hole under one of two identical flat wooden covers that differ only in their location on a tray. In this task the subject must notice and remember where the experimenter placed the reward in each session. As soon as the holes are covered with the boards, a screen is lowered between the experimenter and the subject. After a short delay (usually between 0 and 60 seconds), the experimenter raises the screen so that the tray containing the reward is within the subject’s reach, and the subject must choose which board covers the reward. Another task, referred to as delayed alternation (DA), is similar except that the subject must now learn to alternate its responses from left
