Stroke is caused by an abnormality in brain blood circulation. Approximately 30% of patients present cognitive impairment after brain damage. N400 is an electrophysiological wave that has been related to semantic tasks and the equivalence test. This study’s objectives were to (a) compare the learning of conditional relations and the formation of equivalence classes in patients with stroke with and without cognitive impairment and (b) verify N400’s occurrence and quality under different conditions of stimulation. Two experiments were conducted with 9 participants each, divided into 3 groups: control group, healthy adults; Experimental Group 1, patients with stroke and no cognitive impairment; and Experimental Group 2, patients with stroke patients and cognitive impairment. In Study 1, 9 participants were taught arbitrary conditional relations and equivalence tests. In Study 2, electrophysiological records were made in addition to teaching the conditional relations protocol. The arbitrary conditional relations teaching protocol was efficient, and the equivalence class formation was documented for the control group and Experimental Group 1 but not for Experimental Group 2. In Study 2, Participants P21, P22, and P24 presented the N400 wave’s occurrence in 4 stimulation conditions; P26 in 3 stimulation conditions; P27 and P29 in none of the conditions. The amount of learning and equivalence class formation was directly related to the N400 wave’s quality and occurrence. This corroborates the results from other studies that found that emergent conditional stimulus relations can be considered semantic.