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5.2.1. Four Kinds of Human Interaction

People interact with the world around them in four ways depending on what they are interacting with and the purpose of the interaction. They are:

  Direct manipulation — Handling physical things.
  Language-based communication — Conveying information via abstract symbols.
  Demonstration — Conveying information via a performance.
  Social interaction — Conveying information implicitly, usually about explicit activity, usually via body language.

The important aspects of direct interaction with the physical world are an object’s immediate response to a person’s actions; a wide range of sensory inputs: sight, touch, pressure, heat, sound, and smell; and the use of two hands, arms, feet, body, head, etc., with six degrees of freedom of movement. Support for these aspects of physical interaction within human-computer interaction continue to be very limited, typically: single-handed input with two degrees of movement, two pressure levels (the mouse button), and visual feedback that is often too slow. There are many development efforts to enhance the means of interaction, but they remain cumbersome and uncommon.

The lack of physical interaction techniques with the computer requires the designer to map many real-world actions into a different form with the computer. This changes the nature of the interaction, usually for the worse. For example, a scroll button maps distance to time; the longer the button is held down the farther the displayed information moves. The reader should compare the use of scroll buttons to move about a graphic document with the use of the “hand” cursor, common in graphics applications, that moves the document the same distance as the mouse cursor moves, a distance-to-distance mapping. The performance of the “hand” with its direct distance-to-distance mapping is superior to the scroll button’s time-to-distance mapping for all ranges of movement: short, medium, and long. The designer must carefully consider the nature of each interaction to understand the consequences of such a substitution.

Command-lines, menus, and buttons are the primary computer representations of language-based communication, limited for the most part to simple sentence structures such as noun-verb. Since people converse only with other people, this experience causes people to treat dialogues with machines similar to conversations with people. One aspect of this conversational experience is timing; people get uncomfortable after a pause of 2 to 4 seconds in a conversation whether with person or computer. The use of language with computers also appears to trigger social responses in people (Nass, Steuer, and Tauber, 1994). This social response should be taken into account in designing messages, help, and other language-based situations in the interface.

Demonstration is used when direct manipulation and words are either too abstract or not sufficiently descriptive, such as when showing someone how to slide into a base in the game of baseball. This style of interaction is used with computers primarily for the “watch me” style of scripting in which the user performs some actions that the computer will later mimic. The difficulty with demonstration is in showing all the alternative actions to be used in different situations.

Social interaction deals with the use of cues, signals outside the main communication channel, that help to direct the dialogue. Without them the interaction between people is much more difficult and understanding suffers. For example, just as the listener nods his head or frowns to indicate his reaction to what the speaker is saying, computers need to acknowledge user input with some sort of feedback, otherwise the user is uncertain that the input was accepted. In applications where the computer serves as a communication channel between two people, the computer is most effective when it supports the transmission of the common social cues that people would use if they were face-to-face, e.g., facial expression and hand movement and position.

5.2.2. Reviewing Scenario Flow

The rough layouts should be reviewed with respect to these interaction patterns. The interaction style should feel right for the task and the controls should support the chosen style of interaction. Particular attention should be given to items not covered by the platform guidelines, e.g., the use of transitional animation or the support of social cues. The number of explicit actions that the user must make to accomplish a given task should be minimized, particularly those that just shuffle things around, e.g., opening and closing windows, scrolling, and view changes. After the sketches have been revised, it is time to prototype the primary user scenarios and any interactions that have been developed specifically for this interface.


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