An evaluation of human measures of Kamin blocking : implications for selective attention investigations in schizophrenia
Kamin blocking occurs when learning to one conditioned stimulus is decreased by presenting it in compound with a conditioned stimulus pre-exposed with the outcome. Manipulations of the Kamin blocking procedure are central to current investigations of human learning processes. Additionally, this paradigm is said to reflect selective attention mechanisms and as such is utilised as an experimental model for underlying cognitive deficits in schizophrenia. Different experimental procedures have been independently developed to measure Kamin blocking effects. The relationship between these has not been examined and has important implications for the use of Kamin blocking as an experimental model Two approaches were employed to evaluate the relationship between blocking procedures: to directly compare the association between blocking scores derived from different tasks (Experiments 1-3); and to assess the effect of a trial order manipulation on different task formats (Experiment 4). Specifically, two types of procedure were evaluated: behavioural response and contingency judgement tasks These studies revealed no association between Kamin blocking demonstrated by different experimental formats. However, the different measures were similarly affected by a trial order manipulation. This indicates that a) different measures of blocking may not be driven by the same underlying processes and b) the use of experimental manipulation as assessment of procedural equivalence may not be valid In Experiment 5, significant age and sex differences were observed in blocking effects measured by a behavioural task from the clinical literature. As this task is used as a model for attention deficits in schizophrenia such population factors would need to be taken into account when drawing conclusions about observed deficits in clinical samples Taken together, the present studies indicate that procedural and experimental factors need to be qualified when utilising the blocking model of attentional deficits in schizophrenia. Furthermore, dissociations across blocking procedures could suggest that not all such measures can be assumed to be analogues of selective attention, which should be taken into account in their application to clinical studies.