468 ADAPTATIONS TO PHOTIC QUALITY 



reports digested below, if an ideal investigation is outlined in some detail : 

 You wish to discover whether woodchucks, say, have color vision. 

 Secure your animals, young enough to tame readily, and get them thor- 

 oughly friendly and used to handling while building your apparatus. 

 This must be installed in a quiet room, in uniform surroundings so that 

 no noise, odors, or asymmetrical lighting can serve as cues or be disturb- 

 ing to the animal. The apparatus will be essentially a long, horizontal 

 Y-shaped box, big enough so that the animal can be introduced at the 

 bottom of the Y behind an opaque door, which you can release at your 

 pleasure to let him amble comfortably down the long leg of the box to 

 the junction, there turning either to right or left into one of the wings of 

 the Y. You must be able to tell, visually or otherwise, where he is at all 

 times; but he must not be able to see you while he is in the apparatus, 

 else you may inadvertently give him a cue by your position or expression. 

 As he approaches the junction of the Y he sees lights there, one of which 

 eventually comes to mean to him that he is to turn toward the side on 

 which that light is presented — if he can learn that much, as a woodchuck 

 certainly can. If he makes the proper turn — say, into the right wing — 

 you release a barrier in that wing which allows him to get at a standard- 

 sized small piece of some woodchuck candy or other, perhaps carrot. 

 An identical reward is in the left wing of the box behind a similar 

 barrier so that olfactory cues are balanced for the animal, but if he goes 

 to the left you keep up the barrier and shortly return him to the starting 

 point for his next trial. 



You must not ask the animal to make an absolute reaction, only a 

 relative one. Memory for absolute values is very faulty even for man. At 

 the jimction of the box there must be two stimuli side by side, both of 

 which he can see clearly at all times — even after he has made his choice 

 between them. One of them leads him to food, and is called the positive 

 stimulus. If he turns toward the side where the other stimulus is, he gets 

 no food by thus responding to the negative stimulus. The positive stim- 

 ulus must not be varied in hue or intensity, for if he associates it with 

 food he will probably become greatly upset and bewildered if it is altered 

 in hue or brightness. It must, however, be changed in one way, i. e. as to 

 the side on which it is presented in successive trials. Otherwise the animal 

 will probably fall into a 'position habit', going always to the right or 

 always to the left, having really formed the association 'right = food' or 

 'left = food' instead of the one — 'blue = food', say — you want him to 

 establish. So, the blue stimulus must be on the right and on the left equal 



