Performance and event-related potentials~ERPs! were examined in a proactive interference~PI! task with 15 male schizophrenic patients and 15 matched healthy controls. Within a paired-associate task, 30 pairs of semantically unrelated words~A-B! were presented twice, followed by cued recall, in which the paired-associate B had to be named upon cue A. Subsequently, 50% of the A-words were paired with new words~A-C! and presented in random order together with 15 novel pairings~D-E!. Slower responses and poorer recall of C-than of E-words in the final recall indicated PI in both groups. During acquisition, the paired-associates~C0E! evoked larger P3 and positive slow wave in controls than in patients. During recall, cues~A0D! evoked a slow wave with predominating anterior negativity in controls and posterior positivity in patients. The group-specific ERP pattern suggests deviant encoding and retrieval processes in schizophrenic individuals.

Animals coping with operant conditioning tasks often show behaviors that are not recorded by keys, levers and similar response transducers. Nevertheless, these adjunctive behaviors should not be disposed of by classifying them as incidental. Often they are found to be at least partially influenced by the experimentally programmed contingencies, and under certain conditions they can in turn influence conditioned behaviors. Here we describe the occurrence and characteristics of two such behaviors, stimulus grasping in operantly key-pecking pigeons and intra-delay stereotypies in a delayed matching-to-sample task with budgerigars. It is argued that for a proper account of these behaviors it is necessary to refer to a behavioral systems approach that appeals to longer ranging ontogenetic and phylogenetic histories than is usually considered in the psychological literature. The gaping towards on-key stimuli by pigeons is attributed to the hypothesis that operantly conditioned key-pecks probably relate to a grasp-pecking response that is normally executed towards non-edible items covering food. The intra-delay behaviors shown by the budgerigars are assumed to have originated from stress-induced displacement responses that adventitiously came under the influence of differential reinforcement contingencies. Finally, we discuss what kinds of evidence are needed to put these hypothetical explanations on a more certain footing.

Reduced amplitudes of event-related potentials (ERP) have often been reported for schizophrenic patients. Positive ERPs were examined in 16 schizophrenic patients and 16 controls in a visual paired-associate learning task, in which successful learning of word pairs was evidenced by recognition of "old" versus "new" word pairs. Patients performed significantly poorer than controls. During acquisition the to-be-associated word pairs evoked a P2 and positive Slow Wave (SW) of similar amplitude in both groups. Although the recognition of items as "old" induced larger positive ERPs in controls, ERPs did not vary with recognition in patients. The presentation of the word pairs (50% old, 50% new combinations) evoked a pronounced posterior positive SW in patients but an anterior negative SW in controls. This pattern is identical to the one obtained from a previous paired-associate learning task with cue-recall and suggests that schizophrenic patients are capable of producing large amplitude positive waves under conditions different from those typical for P300 evocation in normals. The larger positive SW may indicate increased effort to compensate for deficient acquisition or association formation.

Performance and event-related potentials~ERPs! were examined in a proactive interference~PI! task with 15 male schizophrenic patients and 15 matched healthy controls. Within a paired-associate task, 30 pairs of semantically unrelated words~A-B! were presented twice, followed by cued recall, in which the paired-associate B had to be named upon cue A. Subsequently, 50% of the A-words were paired with new words~A-C! and presented in random order together with 15 novel pairings~D-E!. Slower responses and poorer recall of C-than of E-words in the final recall indicated PI in both groups. During acquisition, the paired-associates~C0E! evoked larger P3 and positive slow wave in controls than in patients. During recall, cues~A0D! evoked a slow wave with predominating anterior negativity in controls and posterior positivity in patients. The group-specific ERP pattern suggests deviant encoding and retrieval processes in schizophrenic individuals.