| People are able to trade off speed and accuracy when performing a task; that is, they can either focus on performing accurately at the cost of being slow, or on being fast at the cost of decreased accuracy. Performance can be varied along this speed-accuracy tradeoff (SAT) continuum. The present set of studies were designed to, first, test the effects of speed versus accuracy emphasis on attentional processes and the underlying neural activity, and, second, to investigate how the brain achieves the desired level of SAT. In Experiment 1 it was found that attentional adjustments on trials following difficult trials or error trials, and their associated neural activation in the anterior cingulate and lateral prefrontal cortices were modulated by SAT. The conflict adaptation effect and associated anterior cingulate and prefrontal activation were greater under speed emphasis, whereas post-error slowing and associated anterior cingulate and prefrontal activation were greater under accuracy emphasis. Experiment 2 tested how people achieve a desired level of SAT by measuring neural activity in response to cues instructing participants whether to either emphasize speed or accuracy during a subsequent set of trials. Increased activation to speed cues was found in brain regions related to the preparation and execution of actions, which was furthermore sustained throughout speeded performance. This suggests that the level of baseline activation in these areas increased under speed emphasis. Moreover, transient, response-related activation of the dorsal premotor cortices was increased during accuracy emphasis. The results of Experiment 2 support computational theories of decision making according to which evidence for one or another decision builds from a baseline to a threshold, and different levels of SAT are achieved by varying the distance between this baseline and threshold. Together, these studies provide novel data that help us better understand how people are able to regulate their performance. |
