Successful time-sharing depends on the strategy and difficulty of the task in terms of tempo-ral constraints—how many tasks are processed in a given interval—and task complexity—thequantity of information that needs to be processed for a given task.

The first is called thesingle channel theory, which posits that there is limited capacity in the human information pro-cessing system in a time-sharing scenario. When the channel capacity is exceeded, multiple taskstransition from parallel processing to serial processing.

The third theory is information processing analysis theory. Ifat least one task can be carried out automatically, the other task can be carried out with little orno impact on performance (at an appropriate time–error trade-off point).

The second theoryis the multiple resources model, which states that resource limitation concerns the entire systemrather than a channel (Chapter 5).

Ingeneral, perfect time-sharing with no degradation in performance occurs only for tasks that areautomatic, such as speaking while walking.

First, tasks can be time-shared, which implies that the user performs multiple tasks.