Short article Control over speeded actions: A common processing locus for micro- and macro-trade-offs? Ines Jentzsch University of St Andrews, St Andrews, UK Hartmut Leuthold University of Glasgow, Glasgow, UK Cognitive control processes associated with long- and short-term adjustments of human behaviour have attracted much interest recently. It is still unclear, however, whether the mechanisms underlying these adjustments share a common locus within the chain of stimulus – response processing. In order to address this issue, the present study employed a speed – accuracy instruction producing a macro- trade-off, whereas micro-trade-off was studied by means of posterror slowing in reaction time (RT). Participants performed a spatially compatible or incompatible four-stimuli-to-two-response alternative choice RT task. Reliable variations in micro-and macro-trade-off as well as effects of spatial compatibility were found in RT and error rate. Most importantly, posterror slowing was larger when instruction stressed accuracy rather than speed, an effect being independent of spatial compatibility. Because the influence of speed – accuracy instruction and posterror slowing on perform- ance was strongest for response alternations, together present findings suggest that the mechanisms underlying micro- and macro-trade-offs have one common locus at the level of motor processing. Additional influences of macro-trade-off on premotoric processing are likely. A major challenge for human action control is to optimally balance influences of long-term dispositions and short-term needs in response to an ever-changing environment. In the laboratory, long- and short-term influences on behaviour can be studied in speeded choice reaction time (RT) experiments. Long-term changes or macro- trade-offs are usually produced by way of instruc- tion. For example, when instructions emphasize response speed, RT reductions are accompanied by a considerable increase in error rate, whereas RT increases, and error rate decreases when instructions stress accuracy. Thus, participants trade speed for accuracy, and this inverse relation is captured by the speed – accuracy trade-off (SAT) function. However, performance is also influenced in the short-term by the event history, giving rise to so-called micro-trade-offs. One prominent example for such a performance change is participants’ slower and more accurate Correspondence should be addressed to Ines Jentzsch, School of Psychology, University of St Andrews, South Street, St Andrews, KY16 9JP, UK. Email: ij7@st-andrews.ac.uk We would like to thank Rolf Ulrich, Nachshon Meiran, Guido Band, and one anonymous reviewer for their insightful comments on previous drafts of this manuscript. # 2006 The Experimental Psychology Society 1329 http://www.psypress.com/qjep DOI:10.1080/17470210600674394 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY 2006, 59 (8), 1329–1337