In this paper, the authors have tried to simulate variation of human intellectual
concentration employing a cognitive architecture, ACT-R, when they are conducting
a simple cognitive task. Based on the fact that the distribution of the problem-answering
time series of the model varies depending on the structure of the model used for simulation
and the parameter settings, the authors are tackling to reveal how the mechanism
of transition between concentrated and defocused changes depending on human characteristics
and conditions.