Landing reaction of Musca domestica: dependence on dimensions and position of the stimulus.

The functional structure of the mechanism underlying the perception of motion and its processing by the central nervous system has thus far been analysed in the beetle Clorophanuswn<£r(Hassen9tein& Reichardt, i956;Reichardt&Varju, 1959; Reichardt, 1962), in the fly Musca domestica (Hertz, 1934a; Fermi & Reichardt, 1963; McCann & McGinitie, 1965; Bishop & Keehn, 1967) and in other compound-eye animals (Hertz, 19346; Burtt & Catton, 1954; Horridge, 1966; Thorson, 1966; Wallace, 1959). It is of interest therefore to ascertain whether such a mechanism is applied to the perception of more complicated dynamical features. One environmental situation in which flying insects need the perception of one of such dynamical features is during their preparation for landing. When a fly approaches a surface on which to land, at a certain distance from the surface it lifts its first pair of legs to both sides of the head and stretches the last pair backward. This characteristic behaviour has been called the landing reaction; it occurs not only in the house-fly but commonly in all flying insects. Some investigations (Goodman, i960, 1964; Braitenberg & Taddei Ferretti, 1966) of the landing reaction have proved that there are at least two components of the stimulus for landing. One of them is the expansion of a pattern on the fly's compound eye; and it is known that the greatest distance from the pattern at which the fly reacts is proportional to the expansion speed of the pattern. The other is the variation of the light flux coming from the pattern; and it is known that the fly reacts to the decrement of light flux. Generally, patterns which can be expanded involve a change in light flux, thus preventing independent analysis of these two components of the stimulus. An example of such a stimulus is an object running up and away from the fly; change in object area, for a given contrast with the surrounding, involves a change in light flux. Another such stimulus is a cathode ray tube with expanding circles on its screen; the increase in the circumference of the circles increases the light flux. In the present research the two components of the optical stimulus have been separated and the dependence of the landing reaction on each of them has been analysed.