Brain imaging studies suggest that truth telling constitutes the default of the human brain and that lying involves intentional suppression of the predominant truth response. By manipulating the truth proportion in the Sheffield lie test, we investigated whether the dominance of the truth response is malleable. Results showed that frequent truth telling made lying more difficult, and that frequent lying made lying easier. These results implicate that the accuracy of lie detection tests may be improved by increasing the dominance of (...) the truth response and that habitual lying makes the lie response more dominant. (shrink)