VISION 119 



Coccinella and Eristalis. The insects were placed at some distance 

 from a light towards which they walked by a straight path 

 flanked by cardboard walls bearing a pattern of black and white 

 stripes. The insects became regularly attracted off the direct 

 path to the wall which bore a pattern or, if the pattern were on 

 both walls, to that wall which bore the pattern containing the 

 most detail or outlines. There was no difference in effect between 

 vertical and horizontal stripes. 



This capacity for a primitive discrimination of pattern seems to 

 be intimately connected with the responses of insects to visible 

 movements. Hertz (1933) showed that so long as a bee is moving 

 the image of the surrounding objects is moving on the retinulae 

 of the compound eyes. Similarly, a type of pattern with many 

 outlines involves a high frequency of alternating stimuli on the 

 retinulae. Great emphasis is laid on this feature by Wolf (1933), 

 who, as the result of his own experiments with intermittent 

 illumination, suggests that the whole effect of pattern on the 

 insect eye is nothing but that of flickering. 



The two principal qualities of pattern, i.e., the amount and 

 effectiveness of the distribution of outline, also play an important 

 role in the reaction of insects to visible movement. In experiments 

 where an insect is in the middle of a small table around which 

 a cylindrical screen, with black and white vertical stripes, is 

 revolving the animal moves in the same direction. Up to a 

 certain limit the effect increases with the velocity of the movement 

 and with the number of stripes {i.e., the amount of outlines) : 

 this has been shown by Wolf (1933) for the bee and by Gaffron 

 (1934) for flies. Hertz (1934) found that for flies where there 

 are a number of stripes an equidistant distribution of outlines is 

 more effective than an alternation of narrower and broader 

 intervals between the stripes. The best effect to be obtained 

 with the minimum amount of outlines is by means of small spots 

 regularly distributed on the revolving screen. As a consequence 

 of the foregoing experiments, the question arises as to whether the 

 insect is able to differentiate between the appearance of movement 

 resulting from a change of position to surrounding objects and 

 from the movements of the animal itself in relation to such 



