Model Human Processor

Human cognition is often understood in terms of a model of information processing. See section 3.4.2 for diagram and some usages.

Most of this information is presented in The Psychology of Human-Computer Interaction by Card, Moran and Newell.

Components

• Perception
• Motor processor
  • approximately 70 msec cycles
  • Fitts' law: Pointing time (seconds) = 1 + .1 * log2 (distance / size + .5)
• Working Memory (also called short-term memory)
  • Limited approximately 3 chunks
  • Includes perceptual and motor stores
• Long-term memory
  • Essentially unlimited
  • Acquired through active usage of working memory
• Cognitive processor
  • Applies long-term memory to modify working memory
  • Operates at approximately 70 msec cycles
  • Conscious versus unconscious cognition

Constants for keystroke-level model

• K = 0.2 sec Keying: the time it takes to tap a key on the keyboard or a button on the mouse.
• P = 1.1 sec Pointing: the time it takes to move the mouse to a position on the display.
• H = 0.4 sec Homing: the time it takes to move the hand from the keyboard to the mouse or from the mouse to the keyboard.
• M = 1.35 sec Mental preparing: the time it takes to mentally prepare for the next step.
• R Responding: the time needed for the computer to respond.

Issues for discussion

• What does Fitts' law say about sizing and placing selectable items in an interface? Which is better: a couple of medium-distance clicks or one long-distance click?
• What do the keystroke constants suggest for developing an efficient user interface?