It is widely believed that semantic activation from print is not capacity limited (i.e., that it does not need attentional
resources). Prior research has tested this assumption by examining the Stroop effect in the context of the psychological refractory
period (PRP) paradigm. These studies yielded additivity of the Stroop effect and SOA on RT, consistent with the hypothesis
that semantic activation is itself capacity limited (given demonstrations that prior processes are not capacity limited). There
is, however, an alternative explanation for such additivity: performance optimization (Miller and colleagues, 2009). Given
that participants in PRP experiments are told to respond as quickly as possible, they may opt to process serially to improve
performance. We investigated whether additivity of the Stroop effect (standard and semantic) and SOA in the context of PRP
is best explained in terms of a structural bottleneck or performance optimization.