CHAPTER VII 

 Flicker Perception 



Inasmuch as the preceding studies with the chick indicated 

 unequal visual sensitiveness to the spatial details of size and form, 

 there arose the question of the importance of the role played by 

 moving stimuli in the chick's vision. Movement, indicating dan- 

 ger or food, certainly is of great daily importance to the seeing 

 animal. The remarkable ability of birds to discover worms has 

 been plausibly attributed to the visual perception of movement. 

 Might not the chick, then, demonstrate greater perceptual ability 

 if a problem were presented demanding reactions to moving 

 stimuli instead of stationary spatial differences? 



To test the chick's sensitiveness to movement, the same dark 

 room-discrimination method was employed. The stimuli pre- 

 sented were two 6 cm. circular openings illuminated as in the pre- 

 ceding experiments. The sources of these illuminations, however, 

 were attached to an interrupting device by means of which the 

 lights could be made to flash at different, though regular, intervals. 

 The positive rate was adopted as once per second. The negative 

 stimulus was a similar illumination flashing more rapidly. 



To produce these interruptions a rotating disc of wood, one 

 inch thick and four inches in diameter, was used. Bearing upon 

 the circumference of the disc were two pairs of brass points, each 

 pair being in the circuit of one of the source lamps. When one of 

 these pairs of points bore upon a conducting surface, the circuit 

 was complete ; when it bore upon a non-conductor, the circuit was 

 broken. The interruptions of the sources of illumination, then, 

 depended upon an alternation, on the circumference of the disc, 

 between a conductor and an insulator. 



The wooden surface itself provided the insulation. For the 

 conduction, thin bands of brass were firmly fitted and screwed to 

 the circumference of the disc. Thus, a brass band extending half 

 way around the circumference of the rotating disc would provide 

 a complete circuit half of the time. In other words, the lamp de- 

 pending for its illumination upon this band of brass would flash 



