Postural costs of performing cognitive tasks in non-coincident reference frames.

Dual-task interactions in posture and cognitive tasks have been explained as a competition for spatial processing structures or as interference in the online sensorimotor adjustments required for sensory integration. Going beyond these general terms accounts, we propose that interference between spatial and temporal operations in posture-cognition arises at least partly from the need to share a common behavioral context, such as a spatial frame of reference. Using immersive visualization and motion-tracking techniques, we manipulated the spatial reference frames for a standing task and a conjunction visual search task into or out of coincidence. Aside from performance trade-offs due to task-load manipulations, performing visual search in a non-coincident reference frame led to cognitive task and postural task performance decrements (Experiment 1). Postural dual-task decrements were also observed when visual search was split between coincident and non-coincident frames and both frame conditions rendered identical in visual information relevant to posture control (Experiment 2). We concluded that the postural control costs observed for posture-cognition dual-tasking may in part reflect costs of keeping tasks' reference frames in register.