FORM-PERCEPTION IN ANIMALS 135 



factors frequently works serious disturbances. Quite recently 

 Mr. Lashley 2 reported disturbance from the first source. Mr. 

 and Mrs. Watson 3 obtained disturbance from both the first and 

 second factors. Other instances might be enumerated. Suppose 

 an experimenter should obtain failure to discriminate after making 

 such a change as Mr. Hunter suggests. Is there any means of 

 deciding whether the disturbance resulted from the change of 

 " pattern " or from the simultaneous introduction of other 

 novelties ? 



Secondly, with regard to the necessity of any control, which 

 Mr. Hunter assumes: If a human observer place his eye at the 

 exit of the " home-compartment " of the Yerkes box, will not 

 a given form appear against quite different backgrounds and 

 behind quite different foregrounds according as it occupies the 

 right and the left positions respectively ? To the writer it does. 

 Since the stimulus-form is as effective in one setting as in the 

 other it would seem that we are justified in saying that the animal 

 is reacting to the constant form difference and disregarding the 

 variable pattern-difference of the stimuli; using the term pat- 

 tern-difference in Mr. Hunter's way. 



» Lashley, K. S.: Visual Discrimination of Size and Form in the White Rat. 

 Ibid., vol. 2, 1912, pp. 310 ff. 



» Watson, John B. and Watson, Mary I.: A Study of the Responses of Rodents 

 to Monochromatic Light, Ibid., vol. 3, 1913, pp. 1 ff. The disturbance referred to is 

 not reported, having occurred in the preliminary work. The writer received the 

 information directly from the authors and refers to it with their permission. 



