EFFECTS OF SEPTAL AND CAUDATE LESIONS WERE COMPARED ON BRIGHTNESS AND SPATIAL DISCRIMINATION AND REVERSAL. FURTHER ANALYSES OF THE EFFECTS OF THESE LESIONS AND LOW-LEVEL ELECTROSTIMULATION OF THE SEPTAL AREA WERE MADE ON A SPATIAL-ALTERNATION PROBLEM. SEPTAL LESIONS SELECTIVELY IMPAIRED REVERSAL OF SPATIAL, BUT NOT BRIGHTNESS, DISCRIMINATION. CONVERSELY, CAUDATE LESIONS SELECTIVELY DISRUPTED BRIGHTNESS DISCRIMINATION. SEPTAL LESIONS, IN CONTRAST TO SEPTAL STIMULATION OR CAUDATE LESIONS, BLOCKED ACQUISITION OF SPATIAL ALTERNATION AND GENERALLY INDUCED FASTER PERFORMANCE TIME. THESE RESULTS PROVIDE EVIDENCE OF AT LEAST 2 DISSOCIABLE DYSFUNCTIONS ASSOCIATED WITH SEPTAL LESIONS. FURTHER DISSOCIATION OF SEPTAL AND CAUDATE FUNCTIONS IS INDICATED, BUT THE DATA DO NOT RULE OUT SOME COMMONALITY OF OPERATION. (22 REF.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)