a, The relationship between the regulation of stability and flexibility can be investigated by independently and simultaneously varying demands on task focus, via the rate of incongruent trials, and on switch readiness, via the rate of switch trials. b, The rate of incongruent trials modulates the congruency effect but not switch costs, and the rate of switch trials modulates the switch cost but not congruency effects, suggesting independent control of cognitive stability and flexibility. Data from ref.51.