This chapter introduces the notion of rationality. This allows us to provide explanations forinteractive behavior due to users attempting to make the most out of the choices available to them.

The difference between analysis automation—inference—anddecision automation is that in the latter the system must make implicit or explicit assump-tions about costs and values inherent in all decisions.

Decision automation means deciding and selecting appropriate actions among alternatives.This type of automation corresponds to the third human information processing state, decision-making, which the machine is either augmenting or replacing altogether.

Analysis automation refers to the automation of information analysis and involves inferentialprocesses. It corresponds to the second human information processing state: perception/workingmemory.

Acquisition automation corresponds to the first human information processing stage, sensoryprocessing, and it is realized by the system sensing and registering input data.

The third allocation strategy is to allocate each function in a way that maximizes economicefficiency.

The second allocation strategy is assigning each function to the most capable agent, which canbe either a human or a machine.

Therefore, this automation strategy definesthe roles and responsibilities of users in terms of automation instead of the other way around.

First, byautomating everything that can be automated, the user is left with functions that, by definition, thedesigners find hard, expensive, or difficult to automate.

Task allocation is a central challenge in HCI and automation.

First, control can be shared via an extensionthat allows a machine to amplify human ability.

Independently of the chosen strategy, some tasks are to be done by the interactive system andsome by the user. The allocation of such tasks is called functional allocation.

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).

Second, tasks canbe shared in terms of control, which means that some control over the tasks is assigned to anotheragent, such as another user or a machine.

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

A central concern in the design of automation and AI is task sharing.

In all cases, getting the right balance betweenautomation and human control is crucial.

Direct manipulation does not anthropomorphize user interfaces or deskill users.

Software agentsmay allow users to achieve their goals in complex environments with limited expertise.

Automation technology is capable of doing things on its own.

Text entry can also be seen as a task where different subtasks are shared between the human and the computer (Chapter 20).

Persons with varying capabilities and backgrounds need toeffectively enter text, or these systems fail as tools.

Text entry is also a good example of tool use (Chapter 19). A text entry method is a tool that allows the user to communicate with someone or something, typically other people or a service, using asynchronous text messages and longer documents.

The essence of dialogue is that communi-cation is organized in sequences of turns.

Interaction is understood as actions and reactions that minimize the discrepancybetween the present state and the goal state.

Informationtheory provides a rigorous formalism to understand and quantify interaction via the concept ofpassing messages through a noisy channel.

This con-cept, communication of information, is rooted in information theory (Chapter 17).

However, computers can also have goals or at least algorithmic objectives. This adds another levelto teleological determination.

One type of determination is shared by all theories of interaction in HCI: teleological determina-tion.