The central attentional limitation and executive control.

A central attentional limitation is assumed to be one reason why processing costs emerge in situations in which people do two things at once. This limitation causes that processes in two tasks are processed in serial order, if they require simultaneous access to the capacity-limited resource, which is called bottleneck interference. The present article links together recent knowledge about the psychological mechanisms and about the neural implementation of bottleneck interference. First, new findings are reviewed about the location of bottleneck interference in the processing chain, about its relation to the content of the processed information and its dependence on practice. In addition, further new evidence is reviewed that suggests that the bottleneck does not result from a passive occupation of the attention-limited resource by some process. Instead it is suggested that the serial order of processes at a bottleneck results from the involvement of control processes regulating the order of access to the capacity-limited resource. Neuroimaging research suggests that these control processes are associated with activation in regions of the lateral prefrontal cortex, which can be dissociated from the neuro-anatomical implementation of other control functions during dual-task processing.