When learning hurts control: inducing cross-task-covariance causes multitasking costs

Performing two tasks concurrently typically leads to performance costs. Historically, multitasking costs have been assumed to reflect fundamental constraints of cognitive architectures. A new perspective proposes that multitasking costs reflect information sharing between constituent tasks; shared information gains representational efficiency, at the expense of multitasking capability. We test this theory by determining whether increasing cross-task information harms multitasking. 48 participants performed multitasks where they mapped keypresses to four shapes. In a subsequent statistical learning task, these shapes then formed pairs that were predictive or non-predictive of an upcoming target judgement. When participants again responded to these shapes in the multitasking context, performance was poorer when the shape pair had been predictive of target outcomes in the learning phase, relative to non-predictive. Thus, associating common information to shape pairings transferred to negatively impact multitasking performance, providing the first causal evidence for the shared representational account of multitasking performance.