Harold Lasswell

 Who (says) What (to) Whom (in) What Channel (with) What Effect

Lasswell's model of communications is significantly different from those of engineers, including Claude Shannon, and his notion of channel is also different, since it includes different types of media. For example, newspapers, magazines, journals and books are all text media, but are assumed to have different distribution and readership, and hence different effects.

Lasswell's model appears to be a one way model, though the effect is often monitored via a feedback channel, which may not be explicit. For example, do sales of washing powder increase after a TV advert has been put out?