Identifying the Locus of Compatibility-Based Backward Crosstalk: Evidence From an Extended PRP Paradigm

The backward crosstalk effect (BCE) in dual tasking means that characteristics of Task 2 of 2 subsequently performed tasks influence Task 1 performance. This observation indicates that certain features of the second response are already activated to some degree before the first response is selected. Therefore, the BCE challenges bottleneck models, which assume that Task 2 response selection does not begin until Task 1 response selection is finished. Instead, an extended model with a capacity-unlimited response activation stage prior to the bottleneck as the locus of the BCE was suggested. To determine the exact locus of the BCE within the stages of task processing, 5 experiments were carried out. Experiments 1 to 4 were psychological refractory period-like experiments with 3 subsequent tasks. A prebottleneck locus of the BCE was ruled out in Experiments 1 to 3 by using the locus of slack logic. Additionally, a postbottleneck locus of the BCE was ruled out in Experiment 4 by using the effect propagation logic. To further support this latter conclusion, Experiment 5 applied a go-signal manipulation. Taken together, the results of all 5 experiments strongly suggest that the BCE has its locus in the capacity-limited stage, which contradicts the widely accepted notion that a capacity-unlimited stage of response activation preceding response selection proper is the locus of the BCE.