The Kamin blocking effect (KBE) is an established animal learning paradigm measuring selective processing, in which reduced blocking reflects allocation of greater processing resources to non-relevant information. Two KBE tasks are described below. Results from studies using the first (between-subjects) task indicate that KBE is abolished in acute schizophrenics with positive psychotic symptoms. It is also abolished in the relatives of schizophrenic subjects, although interpretation of this finding is hampered by poor performance of subjects in the control condition. The second (within-subjects) task indicated abolition of KBE in schizophrenic patients with positive psychotic symptoms. Administration of acute amphetamine to normal human subjects did not significantly disrupt performance on the first task. Whilst for the second task, although blocking was limited to placebo subjects, overall pre-exposure effects are not sufficiently strong to indicate specific drug effects.