1. The house--fly exhibits the landing reaction when an expanding optical pattern is placed before it.
An expanding pattern which is easy to measure and which keeps the level of illumination constant is created by rotating spirals.
2. In analysing the dependence of landing reaction on the spiral pitch and multiplicity and on the frequency of local stimuli on each ommatidium, (a) interference by the tangential characteristics of the spiral has been observed; (b) stimulus efficiency has been found to depend on stimulus wave-length; (c) the relevance of the above factors and of a temporal parameter influencing both optomotor and landing reactions has been evaluated.
3. The fact that no Moire effect has been observed is explained in terms of characteristics of stimuli used.
4. The dependence of pattern efficiency on the position of the stimulus in the visual field has been ascertained.
5. Spatial integration of local landing stimuli has been shown in various cases and its threshold excitability and saturation point have been obtained. The dependence of these two last parameters on the position of the stimulus in the visual field has been ascertained.