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Journal of Comparative Neurology and Psychology. Vol. XIV.

Plate II.

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SPACE PERCEPTION OF TORTOISES.

By ROBERT M. YERKES. (From the Harvard Psychological Laboratory, Hugo MONSTERBERG, Director.)

The Sense of Support in Animals. A number of investigators have noticed that the young of many animals possess a sense of support, and that their behavior is adapted to the spatial conditions in which they happen to be placed. It is this sense of support that saves the sightless kitten or puppy from falls; but in case of the young chick which similarly hesitates when it approaches the edge of a void visual stimuli apparently determine the reaction. These reactions to spatial conditions are controlled by a complex of sense impressions which is still unanalyzed. In certain animals visual impressions seem to be all-important; in others organic data are chiefly significant, and again in other organisms there are indications of degrees of sensitiveness, if not modes of sense, of which we have no direct knowledge. And so, strange as it may seem, the “spatial worth” of sense data, as James would call it, is no more a matter of accurate knowledge than is the development of the sense of space, or the modes of behavior in different spatial conditions exhibited by any animal.

THORNDIKE ('99, p. 284), who has studied the behavior of young chicks with reference to spatial relations, says “If one puts a chick on top of a box in sight of his fellows below, the chick will regulate his conduct by the height of the box." A chick 95 hours old does not hesitate to jump off at heights of 1 to 10 inches; at 22 inches it often hesitates a long time, and at 39 inches it usually does not jump at all. Furthermore, immediately after hatching, young chicks are able to peck at objects with considerable accuracy, and they apparently estimate distances fairly well before they have had much experience outside the shell.

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