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Speech Recognition and Synthesis

■If a certain action is made available through speech, make sure that tasks involving this action can be completed via speech. If confirmation is required, make sure the user can speak the response (instead of forcing the user to type something, for example). Users prefer to stay in one mode rather than switching back and forth depending on the task.

■For commands that could result in data loss, ask for confirmation before executing the command.

■Don’t make speech the only way for the user to accomplish a task; always provide an alternative method.

Speech Synthesis

The Mac OS X speech-synthesis engine converts any text into highly intelligible, natural-sounding speech. The engine speaks any text sent to it. Developers can send their own text to it using one line of code. In addition, some speech synthesis is automatically integrated into the interface via Talking Alerts, spoken Dock notification, saying the name of certain controls when the mouse points to them, and speaking selected text. Developers should not rely on those features alone, however, because users may not have turned them on in Speech preferences.

Whenever your application uses a system alert sound or other aural cue to deliver specific feedback to users, consider providing the option of using speech synthesis instead. For many users, a spoken phrase is a much more natural and accessible means of communication; it’s a cognitive burden to remember that a particular sound means a particular action has occurred. You can augment the user experience by providing speech feedback in addition to other forms of feedback. In order to accommodate people with special needs, any feedback to the user should be provided in audio as well as visual formats. (See “Universal Accessibility”

(page 37).)

Guidelines for Implementing Speech Synthesis

As much as possible, you should observe the following guidelines when designing your application to support TTS.

258Speech Synthesis

Apple Computer, Inc. June 2002

C H A P T E R 1 6

Speech Recognition and Synthesis

■Use speech synthesis to notify the user of something that happened in the background, such as, “Your download is finished” or “You have a meeting in 15 minutes.”

■When using speech synthesis to notify users that an event has occurred, consider pausing for a few seconds between the visual display of the event—such as a sheet—and the spoken message. Speech is an effective way to get users’ attention only if they are not already looking at the screen, and the delay gives users the opportunity to respond to the notification without hearing any speech. If such a pause is appropriate, provide a way for users to customize its length.

■Provide a way for users to turn TTS on or off within your application and to control such things as volume, voice, and speaking rate.

■Information users enter, such as typing in text fields or selections from long lists, should be spoken back by the computer. For example, if a user types an amount of money, it’s helpful to speak it back immediately to confirm it. Similarly, sometimes users select the wrong item from a list; speech synthesis is a good way to bring this mistake to the user’s attention.

■Speak in response to spoken commands to confirm what was recognized and what action is being performed. For example:

User: Disconnect from the Internet.

Computer: Disconnecting now.

User: Schedule a meeting.

Computer: For what time?

■When testing your application, test with speech on and be sure to listen to all spoken text in your interface. You can override the default TTS of a control by providing an alternative text string.

■Make spoken text sound best by breaking up long sentences and using punctuation effectively, and by using embedded speech commands such as [[emph+]] to focus users’ attention on important information. For technical information, see the Apple developer documentation website.

■Make sure your alerts are well-written and clear. (See “Writing Good Alert Messages” (page 232).) Avoid long sentences and awkward phrasing.

■In applications that make use of characters (human or otherwise) or running commentary, such as games, consider using text-to-speech instead of digitizing voices.

Apple Computer, Inc. June 2002