The time course of the conflict effect in bilinguals and monolinguals

In cognitive control tasks, studies have reported a faster reaction time and a smaller conflict effect in bilinguals as compared to monolinguals. However, these findings are inconsistent across studies and sometimes absent. In the present thesis, the magnitude of the conflict effect was investigated using the response-signal and the stimulation of the motor cortex procedures by eliminating the reaction time distribution differences between the groups. In Chapter 2 (Experiment 1a), a mathematical model was used to investigate the decision processing mechanism in bilinguals and monolinguals by fitting reaction time and accuracy data to the linear ballistic model. The findings indicated no difference between groups and trial types in any of the model parameter estimates. In Chapter 2 (Experiment 1b), a reach-to-touch paradigm combined with the response-signal procedure was used to investigate the magnitude and the time course of the conflict effect in the Simon task. The findings demonstrated similar time points of onset and decay of the conflict effect between the language groups. In Chapter 3, a transcranial magnetic stimulation was used to investigate the time course of the conflict effect in the Simon task by recording motor evoked potentials at the level of the motor cortex. The findings suggested no evidence for the group differences in the magnitude and the time course of the conflict effect. In Chapter 4, a reach-to-touch paradigm was used to investigate the time course of the conflict effect in the Stroop task. The findings showed an early emergence of the conflict effect in bilinguals relative to monolinguals. Together, the results obtained from Chapters (2, 3, 4) provide no evidence for a bilingual advantage in the conflict effect across cognitive control tasks over a broad range of stimulus processing time. The findings are discussed with reference to the current theories of bilingual cognitive advantage.