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International
Organisation for Standardization
Key Feedback
Keytops and spacing
The
keyboard is the principal input device used by operators to
enter information into a computer. Keyboard design can have
a significant impact on efficiency, effectiveness and user satisfaction,
especially in those applications, where the user must perform
rapid and accurate keying operations while looking almost exclusively
at a source document. For this reason, keyboards have been the
subject of extensive study because, the way the keyboard is
laid out, how it functions and the shape of the keys, all affect
user productivity and acceptance.
The
Keyboard Is a Complex Device
The
keyboard is a complex device; it typically possesses over 100
keys generating approximately 120 different symbols or control
characters (not counting capitalized forms) and this makes it
difficult to commit to memory the layout.
In the keyboard, the keys most frequently used, such as the
letters, the numbers, the symbol keys and the standard function
keys, such as Shift, Enter and Backspace, are in the "touch"
area of the keyboard and account for most of the keystrokes
the user makes. Special function keys, such as Esc key and the
directional arrow keys, which are used less frequently, are
in “non-touch” locations and require the user to move the hand
away from the home position to strike them.
Providing feedback or sensory cues to the user is important.
For this reason modern electronic keyboards provide an audible
"click" to indicate that a signal, from the key that has been
depressed, has been received by the system. Conversely, inhibition
or accentuation of the auditory feedback may be used to signal
the user that the keyboard is "locked."
Rapid keying is a complex psychomotor process. A stream of coordinated
signals is sent by the brain to control the muscle activity
that results in key actuations. Several separate muscle activities
may be going on at once: one finger may be completing a key
depression while a second finger is beginning one and a third
finger moves toward a key to be depressed. While all this is
occurring, receptors in the fingers are sending signals that
carry information about the finger movement back to the brain.
This information (feedback) is correlated with what the user
has anticipated as proper feedback.
Top
International
Organisation for Standardization
The
most comprehensive document specifying the characteristics of
the keyboard is ISO 9241-4:1998(E) “Ergonomic requirements for
office work with visual display terminals (VDT)- Part 4, published
by the International Organisation for Standardization (ISO)
in 1998.
ISO is a worldwide federation of national standards bodies (ISO
member bodies). Publication as an International Standard requires
approval by at least 75% of the member bodies casting a vote.
The work of preparing International Standards is normally carried
out through ISO technical committees. International Standard
ISO 9241-4 was prepared by the Technical Committee ISO/TC 159,
Ergonomics, Subcommittee SC 4, Ergonomics of human system interaction.
ISO 9241-4 provides guidance on the design of keyboards used
for typical office tasks based on ergonomic based on ergonomic
factors for keyboard layout arrangements, the physical characteristics
of the individual keys and the overall design of the housing
containing the keys.
The ISO document specifies design requirements for the keyboard
and all its components such as:
- palm
rest
- height
of the home row
- slope
of the keyboard
- keyboard
profile
- finish
of the surfaces
- layout
of the keys
- design
of the keytop
- key
displacement and force
- key
feedback
- key
legends
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Key Feedback
Probably
the most important requirement of the International Standard
is that which relates to key feedback.
Smooth, reflexive keying depends on a user's ability to generate
a pattern of motor signals and to receive information from the
fingers so that a match may be made between intended and perceived
activity. That is why positive feedback from the keyboard is
important for accurate and rapid keying.
ISO specifies that actuation of a key shall be accompanied by
feedback. Feedback can be tactile or auditory. Preference is
given to tactile feedback if the design allows only one method.
The same requirement about feedback is issued by the American
National Standard Institute (ANSI) which specifies that the
actuation of a key shall be accompanied by either tactile or
auditory feedback or both and that, if there is only one, tactile
feedback is preferred.
Keytops
and spacing
Also
very important is the design of the keys. Designed to be comfortable
for the user's fingers, keys typically have a top surface that
is about half an inch square on a three quarter inch center
and have a slightly concave surface. Home position keys may
be more concave than the others so that the typist can sense
by touch that the fingers are properly placed. Keytops may have
a matte finish to prevent reflections from overhead light sources,
making their labels easier to read. The matte finish also makes
the keytop less slippery. Keytops consisting of dark lettering
on a light background are generally preferred and ANSI specifies
a precise reflectance limit for these surfaces.
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