An approach through the looking-glass

Forty food-deprived cockerel chicks were tested individually in a straight runway containing a familiar food cup that moved when the chicks moved. The food cup always moved in the same direction as the chick: For 20 experimental chicks it moved twice as far as the chick; for 20 control chicks it moved half as far. In Lewis Carroll’s (1898/1926) picturesque terminology, the experimental chicks were tested in Alice’s “room through the looking-glass,” in which, in order to approach the food cup, they had to “walk the other way.” Although the control chicks performed well, the experimental chicks evinced the runway behavior that characterizes positive feedback: They persistently chased the food cup away. This means that the spatial polarity of visual feedback is critical and implies that an ordinary approach response is but an automatic (closed-loop) realization of an intended visual perception.