Natural break points: Utilizing motor cues when multitasking

We investigate how people utilize motor preparation time under varying task objectives as a cue to switch between tasks when dialing and driving. Previous research has shown that people tend to switch between tasks at positions where a chunk of digits is retrieved from memory. If the number of chunks is minimized, do people use motor preparation time as a cue to switch between tasks instead? A study was conducted in which participants drove a simulated vehicle while also dialing two phone numbers that contained sets of repeating digits. Participants tended to switch between tasks after typing in a complete set of repeating digits. This effect took precedence over cognitive cues, and was robust when different relative priorities for the two tasks were adhered to (focus on driving, or on dialing). However, when participants prioritized driving they invested more in steering control. Limitations and implications of the work are discussed.