Knowlton, J. Q. (1966). On the definition of "picture". AV Communication Review, 14(2), 157-183.

• Sign and referent categories
  • The concept of sign
  • Sign and referent categories
  • Equivalence and identity
  • Sign and sign vehicle
  • The iconic sign
  • The post-conceptual status of iconic signs
  • The subordinate / superordinate continuum
  • Nonsign visual displays
  • That sign vehicles are independent of their physical attributes for their meaning
• A taxonomy of visual-iconic signs
  • The formal basis of the taxonomy
  • Estimating the potential usefulness of the category set
  • An extrapolation and summary comment