Asymmetries in activation and arousal may contribute to lateralised effects of habituation and contingency learning during a repetitive choice reaction time task.

This study presents experimental data that suggest possible hemispheric asymmetries in contingency learning and habituation following irrelevant or warning stimuli during a discrimination reaction time task. A total of 68 college students participated in a letter-categorisation task (presumably engaging the left hemisphere more than the right hemisphere) and a visuospatial task (presumably engaging the right hemisphere more than the left hemisphere), both of which involved making a decision based on two consecutive stimuli. Without prior knowledge, one group received warning signals contingent with the reaction stimuli, while the other group was exposed to erratic and irrelevant signals throughout the tasks. Analysis of the data showed that a warning signal improved contingency learning in the letter-categorisation, but not in the visuospatial task, while an irrelevant signal led to habituation in the visuospatial, but not in the letter-categorisation task. These results are explained in terms of hemispheric asymmetries in arousal and activation, as originally suggested by Tucker and Williamson (1984).