Kamin blocking is not disrupted by amphetamine in human subjects

An investigation into age and gender differences in human Kamin blocking, using a computerized task

Kamin blocking (KB) is a function within selective attention found to be deficient in schizophrenia. Disparate results in the KB literature, specifically regarding age and gender effects, suggest that we do not yet have a comprehensive understanding of KB in normal human development. The aim of this study is to provide a thorough investigation into the development and occurrence of KB in a normal population. The design replicated and extended a study by Oades, Roepcke, and Schepker (1996). KB is measured using a computer game called the "mouse in the house." Participants must use a joystick to move an icon around a set floor plan, to find a hidden location. These locations are cued by sets of colors, which denote the KB paradigm. Data was collected on 222 participants across 5 age groups (6-8 years; 9-12 years; 13-17 years; 18-21 years; 22+ years). Comparisons were carried out for age and gender effects. KB was observed in all age groups, but there was no significant effect of age on mean KB score. A measure of frequency of participants who showed KB did show a significant increase with age. A significant difference was found between males and females, with females having higher KB score than males. The gender difference was present from the earliest age tested. Our findings suggest significant age and gender differences in the manifestation of selective attention and information processing abilities. This has implications for understanding the development of attention and the understanding of the age and gender dependence of the development of schizophrenia.

The partial reinforcement extinction effect in humans: effects of schizophrenia, schizotypy and low doses of amphetamine

The partial reinforcement extinction effect (PREE) was studied in human subjects. It has been suggested that the PREE depends on neural mechanisms critical to the cognitive dysfunction which underlines acute schizophrenia. We therefore predicted that the PREE should be reduced, through decreased resistance to extinction in the partial reinforcement (PR) condition, in various types of individual: (a) healthy volunteers given low doses of oral amphetamine; (b) those in the acute (but not chronic) phase of a schizophrenic illness and; (c) healthy volunteers with high scores on personality measures of schizotypy. Despite obtaining robust demonstrations of PREE in all experiments, none of these predictions were confirmed. A single, low dose, of amphetamine had no effect on either continuous reinforcement (CR) or partial reinforcement (PR). Acute and chronic schizophrenic patients showed a reduced PREE compared to controls. However this was due to increased resistance to extinction in the CR groups. Finally, high schizotypy scores were associated with greater PREE, attributable to both decreased extinction in the CR condition and increased extinction in the PR condition. The results of these experiments on human PREE provide no support that PREE is a valid paradigm with which to explore the cognitive dysfunction underlying schizophrenia.

Spatial separation of target and competitor cues enhances blocking of human causality judgements

Three experiments were carried out. Each required subjects to make judgements about the causal status of cues following a two-stage blocking procedure. In Stage 1 a competitor cue was consistently paired with an outcome, and in Stage 2 the competitor continued to be paired with the outcome but was accompanied by a target cue. It was predicted that causal judgements for the target would be reduced by the presence of the competitor. In Experiments 1 and 2 the blocking procedure was implemented as a computer simulation of a card game during which subjects had to learn which cards produced the best payouts. The cues that subjects used to make their judgement were colours and symbols that appeared on the backs of the cards. When the target and competitor cues appeared on the same card blocking effects did not emerge, but when they appeared as part of different cards blocking effects were found. Thus, spatial separation of target and competitor cues appeared to facilitate blocking. Experiment 3 replicated the blocking result using spatially separated target and competitor cues.

Associative deficit accounts of disrupted latent inhibition and blocking in schizophrenia

Latent inhibition (attenuated responding to a signal due to signal-alone presentations preceding the signal-outcome pairings) and blocking (attenuated responding to Signal B due to Signal A being paired with the outcome prior to pairings of an AB compound with the outcome) are reportedly absent in acute schizophrenics. The common assumption that these phenomena reflect the normal functioning of attention and the observation that rats administered low doses of amphetamine show a similar disruption has resulted in the development of an animal model of attentional dysfunction in acute schizophrenia. Here, we selectively review the experimental and clinical literature concerning latent inhibition and blocking, their disruption in acute schizophrenia, and the current status of this model. We conclude that the construct validity of the model is compromised if latent inhibition and blocking are viewed in attentional terms because experimental data indicate both phenomena can be better understood in associative terms. We favor a framework in which disruption of latent inhibition and blocking in acute schizophrenics is viewed as an inability to compare and express stored representations (i.e. associative performance deficit). This change of perspective does not undermine the potential value of the model, but rather suggests that the nature of its validity should be reconsidered.

Conditioned blocking and schizophrenia: a replication and study of the role of symptoms, age, onset-age of psychosis and illness-duration

Measures of selective attention processing like latent inhibition (LI) and conditioned blocking (CB) are disturbed in some patients with schizophrenia. [LI is the delay in learning about the associations of a stimulus that has been associated with no event (versus de novo learning); CB is the delay in learning the associations of a stimulus-component when the other component has already started to acquire these associations.] We proposed: (1) to replicate the reported decreases of CB in patients without paranoid-hallucinatory symptoms; (2) to see if CB depends on the age of illness-onset and its duration, as reported for LI. We studied 101 young and old, acute and chronically ill patients with schizophrenia, of whom 62 learned a modified 'mouse-in-house' CB task, and compared them with 62 healthy controls matched for age, education and socio-economic background. CB was more evident in patients with a diagnosis of paranoid schizophrenia than other subtypes. An unusual persistence of high CB scores through testing was associated with productive symptoms (including positive thought disorder). Reduced CB related to the expression of (a) Schneider's first rank symptoms of ideas-of-reference and (b) to negative symptoms like poor rapport and poor attention. CB was less evident in the older patients and those with an earlier illness-onset. In contrast to the similar LI test of selective attention, CB is found in patients with paranoid schizophrenia and its expression is not related closely to illness duration. This implies that the two tests reflect the activity of different underlying processes. We suggest that reduced CB on initial test-trials in nonparanoid schizophrenia reflects the unusual persistence of controlled information processing strategies that would normally become automatic during conditioning. In contrast, continued CB during testing reflects an unusual persistence of automatic processing strategies.

Neuropsychological and conditioned blocking performance in patients with schizophrenia: assessment of the contribution of neuroleptic dose, serum levels and dopamine D2-receptor occupancy

Patients with schizophrenia show impairments of attention and neuropsychological performance, but the extent to which this is attributable to antipsychotic medication remains largely unexplored. We describe here the putative influence of the dose of antipsychotic medication (chlorpromazine equivalents, CPZ), the antipsychotic serum concentration of dopamine (DA) D2-blocking activity and the approximated central dopamine D2-receptor occupancy (DA D2-occupancy), on conditioned blocking (CB) measures of attention and performance on a neuropsychological battery, in 108 patients with schizophrenia (compared with 62 healthy controls). Antipsychotic serum concentration and D2-occupancy were higher in patients with a paranoid versus non-paranoid diagnosis, and in female versus male patients (independent of symptom severity). Controlling for D2-occupancy removed the difference between high CB in paranoid and impaired low CB in non-paranoid patients. Similar partial correlations for antipsychotic drug dose and serum levels of DA D2-blocking activity with performance of the trail-making and picture completion tests (negative) and the block-design task (positive) showed the functional importance of DA-related activity. High estimates of central DA D2-occupancy were related to impaired verbal fluency but were associated with improved recall of stories, especially in paranoid patients. This, the first study of its kind, tentatively imputes a role for DA D2-related activity in left frontal (e.g. CB, verbal fluency) and temporal lobe functions (verbal recall) as well as in some non-verbal abilities mediated more in the right hemisphere in patients with schizophrenia.