Behavior: Basic Psychology of the User - Foundations for Designing User-Centered Systems - page 103

When people are designing displays which involve items that need to be
grouped together they often include them within some form of container (usually a
box). The Gestalt principles suggest, however, that careful placement of the items
will also be sufficient to determine how they are perceived by the user. The laws
also suggest that careful attention needs to be paid to how you lay out items on a
display, because you can, unwittingly, end up with unrelated items being perceived
as being related simply because of their relative placement.
4.6 The Auditory System
For normally sighted and hearing people, hearing is the most important sense after
vision in any interaction. Most people can hear sound in the frequency range
20 Hz up to 20,000 Hz, but both the upper and lower frequency limits tend to
deteriorate with age and health. Hearing is more sensitive within the range
1,000-4,000 Hz, which in musical terms corresponds approximately to the top two
octaves of the piano keyboard, and represents much of the range of the human
voice.
Thus, the stimulus for audition is any vibration that will set the ossicles (small
bones) of the ear in motion between about 20 and 20,000 Hz. Ordinarily, this
means vibrations of the air but vibrations transmitted through other bones (par-
ticularly the skull) also contribute to auditory sensation. (Having a tooth extracted
or drilled will almost convince you that the jaw was designed to transmit vibra-
tions to the ear in the most efficient manner possible!) There are now headsets
available that use direct bone conduction as a way to transmit sound in noisy
environments.
4.6.1 Theoretical Description of Sound
It is convenient to consider the stimulus for sound to be made up of successive
compressions and rarefactions (expansions) of air that follow a waveform over
time. An example is shown in Fig. 4.16 .
Waveforms like that in Fig. 4.16 can be summarized as being made up of sine
waves (they look a lot like the first part of the waveform in Fig. 4.16 but are
smoother and follow the sine function used in trigonometry). There are at least two
reasons for using the sine function. The first is that they are easy to create; a pure tone
produced by an electronic oscillator or a tuning fork follows a sine wave. The second
and more important reason is that theoretically a wave of any shape can be analyzed
into component sine waves. This is known as Fourier analysis. Figure 4.17 provides
a simple example. Work with sine waves thus provides a standard for comparison
across different types of sounds.