Hearing is the second most important sense in HCI. Hearing is a response to air particles that are displaced at a distance from us. Although each particle only moves a tiny fraction, this causes a series of successive variations in pressure. When these sound waves reach the ear, they trigger a series of mechanical pressure changes, which eventually trigger the auditory receptors, causing the sensation of hearing.
Sound waves vary in amplitude (the height of the wave crest), wavelength (the distance between each wave crest) and the frequency (the number of waves per second, measured in Hertz). The loudness of a sound is described in decibels.
Sound is a good way of attracting attention, since people respond more quickly to auditory signals than to visual signals.
| Use the sound system for alerts when: |
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| The information is short and simple |
| The information will not be referred to later |
| For alerts which require the users immediate attention |
| The users visual system is already overburdened |
| The user is moving about from place to place |
| A verbal response is needed |
| Poor illumination makes vision unreliable |