<p>The psychological refractory period (PRP) paradigm has been used extensively to investigate the cognitive processing stages involved in dual-task performance. Interpretations of PRP data have often attributed the difficulty in simultaneously performing two cognitive tasks to a strict serial processing bottleneck in the response selection stage. However, a number of studies have also demonstrated backward response compatibility effects (BCEs) on Task 1 reaction time in dual-task performance, which suggest that response information for Task 2 may be activated in parallel with Task 1 response selection. The goal of this thesis was to examine the nature of the Task 2 processing that operates in parallel with Task 1 response selection in a PRP task, and to consider the implications of this parallel processing for models of dual-task performance. The results of the empirical studies presented here provide converging evidence that the BCE represents automatically activated response information for Task 2 acting on Task 1 response selection. This Task 2 response information can also contribute to Task 2 performance. Models of dual-task performance must account for both the parallel activation of response information and the serial selection of a response for each task.</p> / Doctor of Philosophy (PhD)