was normal. It would be very strange and quite out of accord with the general behavior of animals in labyrinths if a practised rat should be more disturbed by the removal of an accustomed stimulus than an unpractised one. No effect on the learning power of the rats was produced by making their paws anæsthetic (431). Yerkes has shown, although without operating on his subjects, that the Japanese dancing mouse does not necessarily depend on sight, smell, or touch for guidance in the labyrinth (469). It should be noted that proof of an animal's ability to learn a maze when deprived of a certain class of sensations does not show that it normally makes no use of those sensations in the learning process.

As a matter of fact, the stimuli which originally give the "clews" in the case of the white rats must be the rats' own movements. "Muscular sensations dependent on the direction of turning," "kinæsthetic sensations," are the only elements in our own experience that suggest themselves as possibilities where an animal learns the maze equally well when blinded, anosmic, deaf, and partially deprived of touch (431). But this is not the same as saying that when an animal has learned the labyrinth, it is "guided by kinæsthetic sensations." Nor can we show that an animal was not guided by some other stimuli, say visual ones, in learning the labyrinth, when we prove that having once learned it, the animal is not disturbed by the removal of these stimuli. For when the labyrinth path has been learned, the habit may be in a sense quite independent of the very stimuli that served to form it, precisely as the pianist becomes independent of the notes in playing a familiar piece. The fact that Yerkes's frogs were disturbed, after the habit had been formed, by the interchange of the cards, indicates that visual stimuli were still important to them; but if they had not been disturbed by such interchange, when they were fully practised, it would

not have proved that the cards had played no part in forming

the habit.

In the same way, it is not likely that a thoroughly practised animal needs to have in consciousness even kinæsthetic sensations. Watson attempts to describe the processes in the mind of a practised rat as follows: "What leads up to the act of turning? The 'feeling' (probably only vaguely 'sensed ') which may be expressed anthropomorphically in these terms: 'I have gone so far, I ought to be turning about now!"" "If the turn is made at the proper stage . . . the animal may be supposed thereby to get a 'reassuring feeling,' which is exactly comparable from the standpoint of control to the experience which we get when we touch a familiar object in the dark" (431, pp. 95-6). I do not think these before and after 'feelings' are necessarily present at all in the consciousness of an animal whose labyrinth habit is fully formed. Such an animal has become a little machine which takes so many steps along a straight path, turns to the right, takes so many more steps, and so on until the performance is complete. If, indeed, it makes an error in this process, then the kinæsthetic sensations may come into play, but otherwise there would seem to be no reason for assuming in the fully practised animal consciousness of any stimulus except the initial one which starts it on its path.

Very curious are the results obtained by Watson when the entire labyrinth was turned through an angle of 90 degrees. Although no turn which the animals had to take was in any way altered by this proceeding, the rats showed decided confusion, the blind rats as much as the others. This latter fact would indicate that alteration in the direction of the light was not the source of the confusion; but when the maze was rotated through 180 degrees, the blind rats were not

disturbed, while the others were. More investigation, decidedly, is needed before we can decide, as Watson does, "either that static sensations have a rôle, or . . that the rat has some non-human modality of sensation which, whatever it may be, is thrown out of gear temporarily by altering the customary relations to the cardinal points of the compass."

One or two incidental observations regarding the behavior of animals in labyrinths are strongly suggestive of the automatic character of the movements involved. An animal that has gone astray on the path will often find the way back to the starting-point, and from there traverse the whole road rapidly and unerringly (e.g. 450, 431), apparently in the same way that a piano player who has a piece "at his fingers' ends,' but has stumbled in a passage, can go through with entire success if he starts over again. As piano players know, in such a case it is much better not to attend to stimuli at all, but to think of something else; the movements will take care of themselves better if consciousness intervenes as little as possible.

Again, in the process of learning a labyrinth, habits of movement are often formed that are of no use whatever; that do not lead to success, and hence cannot be guided in any sense by the animal's experience of their pleasant consequences. Rouse and Small both report this tendency to form useless habits, and in the case of some salamanders observed by the writer, which never finally mastered the labyrinth they were placed in, habits of going elaborately wrong would make their appearance and persist for several days, each animal remaining true to its individually acquired tendency. The mere fact that the movements were accidentally performed two or three times in succession created a persistence in doing them, although they led to no pleasurable consequences what

ever.

885. Dropping off Useless Movements: the Puzzle-box Method

The dropping off of useless movements is further illustrated in those experiments where animals are required to work some kind of mechanism. This may be called briefly the puzzlebox method. It is obviously an advance in difficulty over the labyrinth method in that it requires the formation of a new

FIG. 16.-Puzzle box used in Porter's work on birds. A B, one method of attaching string to latch; C, a second method. In the first, the loop at B had to be pulled; in the second, the string had to be pushed in.

impulse rather than the mere guidance of an old one; it does not merely direct the animal in the performance of something that he would do anyway, but causes him to do something that he otherwise would not do. Yet the distinction is not so fundamental as it seems.

The puzzle-box method has been tried with birds, rats, cats, dogs, raccoons, and monkeys. Thorndike, its originator, made some experiments of this type on chicks; the animals were confined in pens, from which they could be released by

pecking at a string or some such object. In other cases, as we have seen, these tests should be classed rather with the labyrinth method, as requiring merely that the chick should run out at a given definite place (393). Porter tested English sparrows with boxes containing food, which could be entered by pulling a string fastened to a latch, or by pushing the string into the wire netting with which one side of the box was covered (Fig. 16). The sparrows learned very quickly; one of them by the tenth test had left out all unnecessary movements (344). In later experiments a cowbird and a pigeon also learned to open a similar box. Before beginning the test the birds were accustomed to being fed in the box with the door open. Their first success in opening the door lay in accidentally clawing or pecking at the proper point, and in later trials the action was simplified; thus the birds learned not to attack other parts of the box, to use the bill instead of the claws, and to stand on the floor beside the box instead of hopping upon it. A point of some interest arises in connection with the fact that one or two of the birds, for instance the male pigeon, opened the door in the simplest possible way, although not very quickly, the first time they tried it, and that these birds showed very little improvement in speed through subsequent trials; whereas the ones that had the most difficulty about the first execution of the act ultimately reduced their speed much below that of the others. It is possible, as Porter suggests, that "greater difficulty and therefore more vigorous. activity on the part of the animal in the initial trials of any series may naturally be expected to lead to more rapid progress in the later ones" (345). In Rouse's test of the pigeon by the puzzle-box method, it showed less aptitude than that displayed by the English sparrow (371).

Small tested his white rats with two boxes containing food. One could be entered by digging away the sawdust which was