This report summarizes research concerning stimulus analyzing mechanisms, giving the main experimental findings and theoretical developments. Most of the data and the experimental findings are to be found in the 89 publications listed in the bibliography. The research is discussed under five main headings: (1) shape recognition, (2) selective attention in animals, (3) stimulus generalization, (4) spectral sensitivity and wavelength discrimination, and (5) miscellaneous (performance and amount of information conveyed and visual figural after-effects). (Author/AL)