How conceptual overlap and modality pairings affect task-switching and mixing costs

Manipulating the pairings of stimulus and response modalities has been shown to affect how response selection processes for distinct tasks interact. For example, Stephan and Koch (Psychol Res 75(6):491-498, 2011) found smaller performance costs when participants switched between visual-manual (VM) and auditory-vocal (AV) tasks (modality compatible; MC) compared to between visual-vocal (VV) and auditory-manual (AM) tasks (modality incompatible; MI). However, in the Stephan and Koch study, there was conceptual overlap between one set of stimuli and one set of responses. For the MC pair, these stimuli and responses belonged to the same task, whereas for the MI pair, they belonged to different tasks. To examine how conceptual overlap affected switch and mixing costs, we conducted two experiments. Experiment 1a was a near replication of Stephan and Koch in which conceptual overlap was present in the MC AV task. In contrast, Experiment 1b reduced conceptual overlap within the MC AV task and increased it in the MI VV task. In Experiment 1a, we replicated Stephan and Koch's findings: larger switch costs were observed for the MI pair; in Experiment 1b, we found numerically greater switch costs in the MC condition. In Experiment 2, we reduced conceptual overlap in both tasks and found no effect of modality compatibility on switch costs. However, mixing costs were primarily driven by modality compatibility, regardless of conceptual overlap. These results highlight the different roles that conceptual overlap and modality pairings have on switch and mixing costs.