The Animal Mind: A Textbook of Comparative Psychology

feature of the bee’s visual memory consists in a power of accurately estimating height above the ground. If the entrance to the hive be raised or lowered 30 cm., all the returning bees will go to the old place, and it will be hours and sometimes days before they find the new one. Moreover, the same bees tend to return to the same corner of the opening each time. When a row of hives had been arranged, some with openings in front and others with openings at the side, bees which had been driven home in haste by a storm would sometimes try to enter the wrong hive, but if their home hive opened on the side, they would attempt to enter the foreign hive on the corresponding side (115).

Turner (723 a)*reports that the burrowing bees (Anthophoride) use visual landmarks to identify the location of their nests, and are disturbed if the landmarks are altered. In the solitary wasps, although Fabre is inclined to assume a “‘special faculty” of homing, independent of visual memory, basing his assumption on experiments where the wasps returned to their nests, from which they had been transported in a box to a distance of three kilometers (218, Series I); yet the evidence obtained by the Peckhams seems fairly conclusive in favor of memory for visual landmarks. The solitary wasps have been shown by the observations of the Peckhams to depend upon sight for the return to the nest (572, 573), and the same conclusion is indicated for the social wasps by Enteman (206). The Peckhams’ belief in the visual memory of solitary wasps rests first upon the fact that the wasp, upon completing her nest, always spends some time in circling about the locality, in and out among the plants, as if she were making a careful study of the region. On leaving the nest a second time she omits this process and flies straight away. A

similar “locality survey” is made by hive bees and by social wasps. Secondly, the Peckhams argue that if the wasp does not remember her nest by landmarks, it ought to make no difference to her when the surroundings are altered in any way. They found, however, that a wasp of one species could not discover her nest when a leaf that covered it was broken off, but found it again without trouble when the leaf was replaced. Another wasp abandoned the nest she had made for herself with much labor, because the Peckhams, to identify the spot themselves, drew radiating lines from it in the dust. A third argument against the existence of a special sense of direction is the fact that wasps sometimes are unable to find their nests. In one case the Peckhams dug up the nest of a wasp and she made another five inches away. After an absence of three hours the wasp returned, and seemed to be puzzled as to whether the old spot or the new one were the place of her nest. ‘At first she alighted upon the first site and scratched away a little earth, and then explored several other places, working about for twelve minutes, when she at last found the right spot.” Similarly, when a wasp that was carrying her prey left it for a few moments to go to the nest, as many of them do, apparently to see that all is right there, if any of the surrounding objects were altered she often had great difficulty in finding the prey again. On one occasion a wasp of another species dug its nest in the midst of a group of nests of the Bembex wasp. These latter are usually dug in a wide bare space of earth which has no vegetable growth to serve as a landmark. When the intruder had finished her nest, it looked just like the Bembex holes. She went away, secured a spider, and when she returned she could not find her nest. ‘‘She flew, she ran, she scurried here and there, but she had utterly

lost track of it. She approached it several times, but there are no landmarks on the B. field. After five minutes our wasp flew back to look at her spider,” which she had dropped about three feet away, ‘‘and then returned to her search. She now began to run into the B. holes, but soon came out again, even when not chased out by the proprietor. Suddenly it seemed to strike her that this was going to be a prolonged affair, and that her treasure was exposed to danger, and hurrying back she dragged it into the grass at the edge of the field, where it was hidden. Again she resumed the hunt, flying wildly now all over the field, running into wrong holes and even kicking out earth as though she thought of appropriating them, but soon passing on. Once more she became anxious about the spider, and, carrying it up on to a plant, suspended it there. Now she seemed determined to take possession of every hole that she went into, digging quite persistently in each, but then giving it up. One in particular that was close by the spider seemed to attract her, and she worked at it so long that we thought she had adopted it, for it seemed to be unoccupied. At last, however, she made up her mind that all further search was hopeless, and that she had better begin de novo; and forty minutes from the time that we saw her first she started a new nest close to the spider, as though she would run no more risks” (572). An occurrence of this kind certainly lends color to the ‘recognition of landmarks’ theory. On the other hand, the Bembex wasps themselves find their nests with unerring accuracy, though there is no landmark in the field. Fabre noted that Bembex wasps could not be led astray by any modification of either the look or the smell of their nests, and thought a peculiar form of space memory, unparalleled in our own experience, must be involved in the nest-find-

ing of this species (216, Series I, 263). Bouvier, repeating Fabre’s experiments on Bembex, obtained a different result. When a stone, for example, that had been at the mouth of a Bembex nest was moved a distance of 2 dm., the wasp, returning, went to the stone. Bouvier accordingly maintains the visual landmark hypothesis (99). Ferton holds the same view with regard to a species of wasp that makes its nest in shells. If during successive absences on the wasp’s part the shell is moved from position A to position B, and later from B to C and from C to D, the wasp, returning, goes in turn to each of the positions that the shell has occupied. “In time, she omits to go to A, then to B. Little by little, the image of the previous locations of her nest is effaced in the insect’s memory.” When she has found it, after each displacement, she makes a new “locality survey,” before starting off again (217).

Turner (728) reports that the mason wasp is certainly guided by visual landmarks. A wasp had built her nest on a window casing. The window was one of four in a row; the shades on the other three were down. When the shade on the window where the wasp’s nest was situated was drawn down and that of the next window drawn up, the wasp returning sought her nest on the casing of the next window, which was now the only light one in the row. Solitary wasps and bees, which need to find their way back, not to a nest whose position remains fixed, as is the case with ants and honey bees, but to nests in new positions from day to day, almost certainly have to depend upon their recognition of visual landmarks, and hence we have another evidence that the compound eye can give a serviceable image.

That carrier pigeons depend on visual landmarks is maintained by many authorities. They do not fly at night, nor do they home well in cloudy weather. Young pigeons have to be trained on short distance flights, though of course this might be the case if they depended on some other power than recognition of visual landmarks. Mi- grating birds in some cases fly long distances over the ocean, where no visual clues can be furnished. Watson (769) caused some noddy and sooty terns to be carried in a steamer from the Tortugas Islands to the latitude of Cape Hatteras, a distance of nearly a thousand miles, where they were liberated. The locality is far out of their range of habitat, yet they returned to their breeding place in about a week. Hachet-Souplet+ suggests that a very vague visual image, of objects too far off to be clearly seen, may be used in such long distance homing, but the curvature of the earth would interfere with a bird’s getting even a vague image of any surroundings that could be familiar to it.

The factors that make possible the perception of the third dimension, depth, or distance outward from the body, in invertebrate animals are little known. Certain invertebrates do give evidence of. the power to judge distance. The hunting spiders, for example, which do not make webs, but pursue their prey in the open, leap on it from a distance of severalinches. Dahl thinks their distinct vision is limited to two centimeters (168), and Plateau says capture is not attempted until the prey is within this distance (596). The Peckhams, however, tested a hunting spider by putting

1VI Congrés Int. de Psychologie, 1909, p. 663. Ihave been unable to obtain the original article. it at one end of a narrow glass case sixteen inches long, at the other end of which a grasshopper was placed. When eight inches from its victim, the spider’s movements changed, and at four inches the leap was made ! (571). Reactions of this character, where the animal makes a single movement adapted to the distance of an object from it, are almost the sole evidence we can get of accurate perception of the third dimension. The alleged performance of the jaculator fish, which, as described by Romanes, “shoots its prey by means of a drop of water projected from the mouth with considerable force and unerring aim,” the prey being ‘‘some small object, such as a fly, at rest above the surface of the water, so that when suddenly hit it falls into the water,” would involve distance perception (640, p. 248). The catching of insects on the wing by various amphibians, reptiles, and birds has the same significance. A salamander cautiously stalking a small fly will not strike until it gets within a certain distance. In Necturus and in other animals the pause just before snapping at food has been suggested to be for the purpose of proper fixation (785).

Training an animal to jump from one support to another is a method that has been used to study distance perception in the mouse (775) and white rat (634). Waugh put a mouse on a disk and raised it a certain distance above a support; he then measured the time the mouse hesitated before jumping, when the height of the disk was varied. From the fact that the mice hesitated longer, the greater the height, he inferred some visual perception of distance.

1 Porter observed that the distance at which spiders of the genera Argiope and Epeira could apparently see objects was increased six or eight times if the spider was previously disturbed by shaking her web (612). This, of course, does not refer to the power to judge distance. When, however, the mice were required to judge which of two partitions was nearer to their starting-point, and to turn to the right or the left in accordance with this preliminary judgment in returning to their nest, they failed: this really involves a rather complex type of learning, and is a much less fair test of the mere ability to perceive distance than is the instinctive reaction of jumping. In Richardson’s (634) study of the rat, the animals were trained to jump from one horizontal support to another. They proved able to judge quite accurately the direction of the platform to which they had to jump, but when its distance was altered they could not adapt themselves, and jumped either too far or too short.

Yerkes’s tests of the so-called ‘sense of support’ in tortoises indicate, like Waugh’s experiments on the mouse, some power of estimating distance by vision in these animals. He experimented, it will be remembered, with individuals belonging to three classes: Jland-dwelling, water-dwelling, and amphibious. The first mentioned would crawl off the edge of a board 30 centimeters above a net of black cloth only with much reluctance when their eyes were uncovered; when blindfolded they would not move at all. The water tortoises plunged off without hesitation from a height of 30 centimeters, but hesitated slightly at 90 centimeters, although some individuals would take the plunge at once even from a height of 180 centimeters. When blindfolded, all of the water tortoises rushed off at any height. The land-and-water-dwelling tortoises hesitated at 30 centimeters and at 90 centimeters showed a conflict of impulses, trying to catch themselves before launching off. When blindfolded they would not leave the board at all, though they moved about upon it freely (810).

Some of the most important conditions of distance perception in our own experience are lacking in the lower vertebrates and in invertebrates. Stereoscopic vision, the appearance of solidity given to objects by the fact that the visual fields of the two eyes combine, thus producing blending of two slightly different views of the object looked at, has been held to be dependent on the partial crossing of the optic nerves on their way to the brain, whezeby each retina sends:nerve fibres to both hemispheres of the brain. This arrangement does not appear in the animal kingdom below the birds; whatever function it plays in space perception is, then, absent from reptiles, amphibians, fish, and invertebrates. Certainly stereoscopic vision cannot exist in animals whose eyes are so placed that the same object cannot be seen by both, as is the case with most fishes. In birds whose eyes are situated too far toward the sides of the head for the same object to cast its images on the foveas or centres of the two retinas, there appears to be a secondary fovea in each eye, so placed as to suggest that it serves binocular vision, while the primary fovea is used for monocular vision. In certain mammals the eyes are placed so far towards the sides of the head that the binocular field is very small. This is probably the reason why rodents do not have a more accurate perception of distance. The writer made some simple tests on the use of binocular and monocular vision by the rabbit (756). When the animal was sitting quietly, two bits of food of equal size and kind were held at equal distances from the rabbit’s nose, one straight in front, the other directly to the right or left of the rabbit’s head.

In forty-eight out of fifty trials, the rabbit turned towards and secured the food at the side rather than that in front, thus showing its dependence on monocular rather than binocular vision. Convergence, the turning of the eyes toward each other to bring the two images of an object on the central part of the retinas, which is an important aid to human estimations of distance, is also necessarily lacking in animals without binocular vision. A third factor in our own perceptions of distance, the accommodation of the crystalline lens, that is, the alteration of its convexity through the pull of the accommodation muscle to enable it to focus objects at different distances, has been carefully studied in connection with the lower animals by Beer. Through experiments on the refractive powers of eyes dissected from the dead animal, he reached the conclusion that no invertebrates but cephalopods have the power of accommodation. It is rudimentary or lacking also in some members of the fish, lizard, crocodile, snake, and mammal families. In cephalopods, fishes, amphibians, and most reptiles, the process of accommodation does not involve a change in the form of the lens, but an alteration in the distance between the lens and the retina. The device of increasing the curvature of the lens for vision of near objects appears first in certain snakes, and is found throughout the higher vertebrates (33, 34, 35, 37)-

Where accommodation does not exist, as in most invertebrates, it is possible to trace other arrangements for adapting vision to the distance of the object seen. Thus in compound eyes, part of the eye may be adapted to near vision and part to far vision. This is suggested by the fact that some of the little tubes, or ommatidea, of which the compound eye is composed, diverge from each other by a less angle than others, indicating that they are suited to the reception of more nearly parallel rays. In insects with both simple and compound eyes one form may be used for near and one for far vision. It has been main-

tained (182) that the simple eyes function with the compound eyes to respond to changes in the depth of objects, since such changes would alter the angle at which light rays from the object would fall on the two sets of eyes. Spiders appear to have the principal eyes adapted for far vision and the auxiliary eyes for near vision, while one spider, Epeira, has part of the hinder median eye adapted to each (324). The temptation is strong to speculate upon the essential nature of the conditions which make possible true space perception, the simultaneous experiencing of sensations that are referred to different points in space. Such speculation must be of the most tentative description, yet the following suggestions seem not wholly unwarranted by the facts. For one thing, it looks probable that the ability to suspend immediate reaction is essential to space perception. Can a spatial complex of sensations occur in the experience of an organism unless that organism is capable of receiving a number of stimuli on a sensitive surface and of suspending, for a brief period at least, all reaction? Let us take as an example of such a complex a visual field, within which different color and brightness qualities are arranged in definite order, some above, some below, some to the right, others to the left. Could such a balance of tendencies to move the eye as is involved in the simultaneous perception of a number of elements preserving regular space relations to each other have been brought about unless no single one of the tendencies were irresistible? One can readily imagine an eye functioning in such a way that every stimulation of it, though occa-

sioned by rays from several different directions acting simultaneously, should issue at once in a resultant movement. Would not the accompanying consciousness be a single resultant sensation, rather than a complex of spatially ordered elements? It is a good deal easier, of course, to ask than to answer such questions. Again, the power of getting true spatial images seems to be bound up closely with the power of moving the sensitive ' surface. We get our best tactile space perceptions through active touch, involving movement of the hands and fingers ; our visual space perceptions are profoundly influenced by eye movements. Where the movements of an animal’s body as a whole are very rapid, as in the case of winged insects, this fact may compensate for the immovability of its eyes. Forel, as we have seen, thinks that insects which can explore objects by moving the antennez, bearing the organs of smell, over them, may have smell space perceptions, such as are unknown to our experience; they may perceive the shape and size of odorous patches as we could do if our organs of smell were on our hands (233). Now, movement of a sense organ brings about the same result that movement of a stimulus across a resting sense organ does; that is, the stimulus affects different points of the sensitive surface in succession. But the vital significance of the two is quite different; movement of an object across a resting sense organ means very likely that the object is alive; it must be instantly reacted to, and the speed of the reaction is unfavorable to the formation of a true space perception. Movement of the sense organ, however, gives a series of impressions on successive points of the sensitive surface, from a resting object. While the sense organ is being moved, it is probable that other reactions of the animal will be suspended. Whether any part in the forma-

tion of that complex conscious content which we call a spatial image, consisting of different sensations simultaneously apprehended, is played by the “‘lasting over” of the impressions on one sensitive point after the stimulus has passed on to the next, a phenomenon which we find both in touch and in sight sensations, it is impossible to say. We are, however, apparently justified in the statements that the essence of space perception, as distinct from other conscious processes that may accompany spatially determined reactions, is the presence of an image in the sense above defined, and that a movable sense organ is an important condition for the production of such an image.

THE reactions of animals to stimulation show, as we review the various animal forms from the lowest to the highest, | increasing adaptation to the qualitative differences and to the spatial characteristics of the stimuli acting upon them. It is therefore possible to suppose that the animal mind shows increasing variety in its sensation contents, and increasing complexity in its spatial perceptions. But besides this advance in the methods of responding to present stimulation, the higher animals show in a growing degree the influence of past stimulation. While a low animal may apparently react to each stimulus as if no other had affected it in the past, one somewhat higher may have its reaction modified by the stimulation which it has just received. An animal still more highly developed may give evidence of being affected by stimuli whose action occurred some time before; and finally, in certain of the vertebrates, perhaps, as in man, conduct may be determined by the presence in consciousness of a memory idea representing a past stimulus. ‘Learning by experience,” or “associative memory,” as we saw in Chapter IT, has been regarded as the evidence par excellence of the existence of mind in an animal. That it does not serve this purpose to entire satisfaction was also pointed out in that earlier chapter, and will be more clearly apparent as we survey

in the following pages the various ways in which an organism’s past experience may modify its behavior. For each type of modification we shall try to find a parallel in human experience, and thus to interpret, so far as possible, the conscious aspect of the learning process. To begin with, we shall distinguish between those modifications which depend on some comparatively lasting alteration in the organism (in its nervous system if it has one), that is, the kind of modification which is ordinarily understood by the term “learning”; and modifications which are due to a change essentially temporary in its character, in the physiological state of the organism. Even in the lowest animals the effect of a stimulus depends on the organism’s physiological condition, and this condition is often the result of stimulation recently received.

§ 71. Modifications Due to Essentially Temporary Physiological States: (a) Heightened Reaction as the Result of Previous Stimulation. Sometimes the effect of the stimuli which the organism has just received increases the violence of its response to a given stimulus. Thus in the earthworm Jennings points out that various stages of excitability may exist, due to the action of previous stimulation, and varying all the way from a state of rest, where a slight stimulus produces no effect, to a condition of violent excitement, where moderate stimulation will cause the animal to ‘‘whip around”’ into a reversed position or wave its head frantically in the air (377). This increased excitability suggests the ‘‘nervous irritation” produced in a human being by an accumulation of disagreeable stimuli; an increased feeling of unpleasantness accompanied by more diffused organic

and kinesthetic sensations is its accompaniment in the human mind. When the same stimulus is repeated, in many cases the effect of this heightened excitability is shown by the organism’s performing in succession different forms of the negative reaction until one of them is successful in getting rid of the stimulus. The ciliate Stentor furnishes us with an example. When attached by its stem, if it is strongly stimulated, say, with a glass rod, several times in succession, it first tries its commonest negative reaction, bending over to one side. If the stimulus continues, it reverses momentarily the direction in which the cilia are whirling. If this, several times repeated, does not succeed in getting rid of the stimulus, the animal contracts strongly upon its stem. This also is continued for some time, but if the stimulus too is kept up, the Stentor finally breaks from its moorings and swims off (370).

There are many examples of similar behavior in other animals. Hydra in certain cases tries first the ordinary negative response of contraction, and later moves away from the region it has been occupying (751 a). Frandsen found that if the slug Limax maximus has a tentacle touched several times in succession, it at first withdraws the tentacle and turns away from the stimulus. Later, it may move toward and push against the stimulus, and do the same if the touch is on the side of its body, resisting and curving around the obstacle — another way, of course, of getting rid of it (236). Preyer, again, observed a very pretty instance of this sort of behavior in the starfish. He. slipped a piece of rubber tubing over the middle part of one of the arms of a starfish belonging to a species in which those members are very slender, and found that the animal tried successively various devices to get rid of the foreign

body, to wit, the following: rubbing it off against the ground, shaking it off by holding the arm aloft and waving it pendulum-wise in the air, holding the tube against the ground with a neighboring arm and pulling: the afflicted arm out, pressing other arms against the tube and pushing it off, and, finally, as a last resort, amputating the arm. - This, says Preyer, is intelligence, for the emergency is not one normal to the animal, and it is adapting itself to new con- _ ditions (617). It would, however, be demanding too much _ even from intelligence to suppose that the starfish’s behavior jis entirely new. A human being, capable of ideas, could “enly, in a similar predicament, “think of,” that is, call up, [ ideas of the behavior which on former occasions somewhat \zesembling the present had proved effective. Do such cases of the trial of different devices indicate that the animal concerned calls up any kind of idea or image of each device before putting it into practice? Decided evidence in favor of such a supposition might be furnished if the “trial and error’ needed to be gone through with only once. A human being brought into such conditions and guiding his conduct by ideas would, if placed in a similar emergency soon afterwards, immediately recall the idea of the successful action and waste no time over the unsuccessful ones. But we have no reason to think that such is the fact with our primitive animals. Preyer’s starfish, when confined by large flat-headed pins driven into the board on which it lay, close up in the angles between its arms, managed to escape by trying a large variety of movements, and gradually diminished, Preyer says, the number of useless movements made in successive experiments (617). O. C. Glaser, on the other hand, found that the echinoderm Ophiura brevispina does not improve at all with practice in removing obstructions from its

arms. The very versatility of the starfish, this writer thinks, tells against its perfecting any one movement through experience (260). Stentor and Hydra go through the same series of reactions each time, without apparently being influenced by their previous behavior. And again we must remind ourselves that there is no reason why their conduct, adaptively regarded, should be otherwise. Anj animal with so little power of distinguishing qualitative differences among stimuli cannot be in any way awar that the stimulus which affects it a second time is going, as in the previous case, to be so persistent that the ordinary: negative reaction will not get rid of it. Further, each re action of the series performed by the animal is more dis4j turbing to its ordinary course of life than the preceding one. The Stentor can bend to one side and still continue the food-taking process; if it reverses its ciliary action, feeding must be momentarily interrupted; while contraction on the stem and breaking loose from its moorings are sti more serious infractions of the normal routine. It woul be decidedly disadvantageous to take the last step whil there was any chance that milder measures might prevail In all probability, since the behavior just described has, no permanent effect upon the animal, it is physiologically; due, as Jennings suggests (375), to the overflow of the ner-/ vous energy set free by the stimulus into first one channel and then another. In most cases the movements resulting | are all adapted to getting rid of the stimulus, though only, one of them is successful in so doing ; but we have on record ' one case where, in a supreme emergency, the stimulus, being not only repeated but increased in intensity, ever possible outlet: is tried, whether it has any fitness to thy situation or not.

This was observed by Mast, testing the effect of increased temperature on the reactions of planarians. The first influence of such increase from 23 degrees to 26 degrees C. is to produce heightened activity and positive reactions. Then, from 26 degrees to 38 degrees, the reactions are negative. From 38 degrees to 39 degrees, violent crawling movements set in, and then, curiously enough, the righting reaction is given, perfectly irrelevant, of course, to the conditions. Finally, the anterior and posterior ends are turned under, the central part is arched upward, and the animal falls over forward on its back (462).

In all these cases where repetition of the same stimulus produces successively different forms of the negative reaction increasing in violence, it is most natural to think of the psychic accompaniment as an increasing degree of unpleasantness. In our own experience, repeating a stimulus does not alter the quality of the resulting sensation, except where the structure of a special sense organ is a modifying factor, as in the case of visual after-images. A decidedly disagreeable stimulus acting repeatedly on a human being may produce unpleasantness that grows more and more intense until it is unbearable; the behavior of a human being under such circumstances is much like the anirnal behavior we have just been describing. Various movements calculated to get rid of the stimulus are tried, each more energetic than the last. Hence, if the lower ‘animals behaving thus are conscious, we may plausibly assert that their consciousness under these circumstances is increasingly unpleasant. But the human experience in such a case would be, or might be, further characterized

y the presence of ideas. That is, the human being would think of the different ways to get rid of the stimulus , one after another. This, many, at least, of the animals that try different negative reactions are apparently incapable of doing. We judge that they are so by the simple. fact that on being subjected after an interval to the same presumably disagreeable stimulus, they do not at once make the reaction that was previously successful in getting bt

rid of it. A human being, recalling that reaction in idea, would be able to do so. We shall see in the next chaptet | that many animals, while they do not learn the successful) reaction from a single experience, do gradually diminish the number of unsuccessful ones made in a series of experiences. It is quite possible that this will prove to be true of all animals, as experimental evidence accumulates. § 72. Modification Due to Essentially Temporary Physiological States: (b) Cessation of Reaction to a Repeated Slight Stimulus.

The type of modified response just described occurs\ when the stimulus is strong, and presumably injurious. | When it is of moderate intensity only, the organism tends to respond less and less violently as the stimulus is repeated at short intervals, until finally the response lapses entirely. The Ciliata Vorticella and Stentor, which spend a part of their time attached to solids by a contractile stem, contract at the first application of a moderately intense mechanical stimulus, but fail to react at all when the stimulus is several times repeated (370). Hydra responds to mechanical stimulation by contraction, but gets used to the process when repeated and gives no further reaction (751a). The sea-anemone Aiptasia reacts by a sharp contraction to a drop of water falling on it; later it ceases its response to this stimulus. If exposed to light, it contracts and remains in this state for some hours, but afterwards expands again (374). The annelid Bispira voluticornis