Designing Effective Speech Interfaces

Human Limitations

The second law is Human Limitations: The interface will not overload the user's cognitive, visual, auditory, tactile, or motor limits.

Human Factors

Humans have cognitive, visual, auditory, tactile, and motor limits on the quantity and quality of information that they can process. For an interface to be easy to use, it cannot overload any of these limits.

Memory

People can remember between five to nine things for about 20 seconds in their working or short-term memory. To remember more than that, the information must be chunked in some way, so that they are required to remember less, or the information must be semantically coded or given a meaning. For example, this string

eibjwlfikqqk

is seen as 12 separate letters because it has no meaning. But this string

dogcatcowpig

is read as four chunks or four separate words. The latter is easier to remember than the first because there are only four items to remember or memorize. It is also easier to remember because it is semantically coded—the letters create meaning by being the names of animals (Sanders and McCormick, 1993, 67).

The easiest information to remember has three to four chunks with three to four items per chunk.

The easiest information to remember has three to four chunks with three to four items per chunk. Sanders and McCormick (1993, 67) discuss the research of G. Miller. His article, originally published in 1956, is “The Magical Number Seven, Plus or Minus Two” (Miller, 1956). Miller found that ...