Alerts and feedback should be provided in as many channels as possible, to help assure perception and XXXXX.
Haptics refers to receiving information by touch. Practically, with current generally-available technology, this refers to the use of vibration to communicate with the user. In much the same way that mobiles have evolved to contain a variety of sensors, they also have a broad range of output devices; most mobiles have some sort of vibration, or an external speaker, which can be used for at least basic Haptic Output.
These vibrations are generally propagated through the entire device, but can be localized, or placed only in specific components, such as the pen in a Pen Input device.
Most vibration is very coarse, and accomplished by a simple off-center weighted motor. Control is only by intensity and switching the motor on and off. Transducer-based vibration is also available, using tools typically employed for audio output to make more nuanced vibrations. This may simply involve the bone conduction transducer (BCT) included for use of hearing impaired users being re-purposed for general Haptic Output. Use of the BCT for audio output is not part of this pattern, and is otherwise beyond the scope of this book.
In addition, the device speaker can generate tones that vibrate more than they are emitted as audio, and thereby fall more into the Haptic Output range than that of Tones despite the output device being used.
Additional methods of haptic output are being developed in the laboratory, and may appear in production soon. These include the ability to sense objects that are not physically present, enabling tactile virtual keyboards for example.
For mobile devices, Haptic Output is currently used in two ways, both distinctly as dynamic output methods.
Response -- When the user makes an action, the device confirms it has received and understood the action, and makes it seem more real by adding a response. Most typical is a "click" when virtual buttons are used, but any action may use this, including scrolling, gestures (the system indicates when a complete gesture is accepted) and even for the use of physical buttons.
Notification -- Alert lights and tones, used to notify of events when out-of-context, may be emphasized or replaced with haptics. Vibrate is heavily used for this, and has been long enough it is a well-understood pattern by the general population. Vibration helps users detect alerts when the sound is off or muffled, and can help to localize the device when in a pocket or purse. For additional details, especially on display in other channels, see Notifications and Tones.
As discussed above, haptics may soon also be used for other types of tactile output. Especially useful will be the ability to detect shape and texture -- to allow feeling virtual, on-screen elements. This will form a third variation, of output perceived by the user to be passive, and representing static, physical spaces and objects.
Haptic Output is used to emphasize that an action happened or communicate in other channels when users may not notice audio or visual cues. They must never stand alone, and must be used to reinforce actions by the user, reactions on screen or displays on screen, by LED or by audio.
...Phenomena like the McGurk effect -- where speech comprehension is related to the visual component -- appear to exist for other types of perception. Tones should support interaction with the visual portions of the interface. ... and also make sure you don't vibrate once then not again, could be written off as a phantom ringer...
...VIB ALERT must always correspond to at least one visual or tactile component. If an alert sounds, it should always have a clear, actionable on-screen element. These should always appear in the expected manner for the type of event. Feedback tones correspond to keypresses or other actions the user takes, and alert tones should display in the conventional method the device uses for Notifications.
Haptic Output for Notifications (to include ring tones) is generally considered to be contiguous with the volume control system. Vibrate is either the setting between off and the lowest level, or can be enabled as a switch so it is on (or off) at all volume levels. While being used, vibration will be silenced in the same manner and at the same moment as Tones or Voice Notifications are. The same mute, cancel or silence functions will be presented when only vibration is enabled, and there is no audio output.
Vibrate isn't fixed, but should mean something, feel like a click when a click, feel harsh when "bad" feel soothing when "good" etc.
like sound... mean something... preferably emulate real items, such as key clicks or the texture of the item being dragged across...
--- >>>> The tone must correspond to the class and type of action and should imply something about the action by the type of tone. Clicks denote keypresses, whereas buzzers denote errors for example.
...Sound design is an entire field of study. If sounds must be created from scratch, a sound designer should be hired to develop the tones based on sound principles. Be sure to denote the meaning -- and emotional characteristics -- for each sound.
...Vibration and audio are closely coupled, so should be considered hand in hand. If Tones are used in concert with Haptic Output, assure they do not conflict with each other. For devices without haptic or vibration hardware, audio can serve this need in a limited manner. Short, sharp tones provided through the device speaker can provide a tactile response greater that their audio response.
... The illusory continuity of tones can be exploited in a manner similar to how persistence of vision is for video playback. Simple tones can be output with gaps or in a rapid stairstep and be perceived to be a continuous tone. This is especially to simulate higher fidelity audio than can be achieved on devices with constrained processing hardware. ????????
... Do not allow alerts or other Tones to over-ride voice communications. Many other types of audio output, such as video or music playback, may also demand some tones be greatly reduced or entirely eliminated. Do not play multiple tones at one time.
Vibration and sound are closely coupled behaviors and can influence each other in undesirable ways. When both are needed, they generally must be alternating to avoid conflicting with or modifying each other. Alerts, for example, generally vibrate briefly, then sound a brief Tone, and repeat this until the notification alert time expires or the user cancels or mutes the output.
Do not over-use haptic output without a good understanding of the device hardware. If traditional motor-driven vibration is used, it may consume the battery excessively quickly.
Haptic output can easily induce "Alarm fatigue" in the same manner as for alert Tones. If the alert method is too generic, too common or too similar to other tones in the environment (whether similar to natural sounds or electronic tones from other devices) they can be discounted by the user. Use as few different sounds as possible, but avoid using simple "vibrate" for every alert. Note that disregarding alerts is not always deliberate, and can eventually result in users sleeping through alarms that are quite intrusive due to the tone or vibration being considered noise by their brain.