.NP
 can be varied from a (confidential) whisper to a¬
(loud) shout
 .NP
 requires very little energy
 .NP
 is not appreciably affected by weightlessness or¬
vibration.
 .LE
 However, these either derive from the three¬
advantages we have discussed above,
 or relate
 mainly to exotic applications in space modules¬
and divers' helmets.
 .pp
 Useful as it is at present, speech output would¬
be even more attractive if it could
 be coupled with speech input. In many ways,¬
speech input is its "big brother".
 Many of the benefits of speech output are even¬
more striking for speech input.
 Although people can assimilate information faster¬
through the eyes than the
 ears, the majority of us can generate information¬
faster with the mouth than
 with the hands. Rapid typing is a relatively¬
uncommon skill, and even high
 typing rates are much slower than speaking rates¬
(although whether we can
 originate ideas quickly enough to keep up with¬
fast speech is another matter!) To
 take full advantage of the telephone for¬
interaction with machines, machine