. The wonder of life . ng, of forming associa-tions, of profiting by experience, of experimenting in novelsituations, and so on. Association.—It was a great step in evolution whenanimals began to associate sensations together. We meanby a sensation, physiologically, an impression made on thenervous system by external stimulus, and psychologically,an awareness (to some degree) of the external us refer briefly to some of the experimental work whichhas been done in the study of the association of is, for instance, the work of Pavlov and his schoolon the establishment
. The wonder of life . ng, of forming associa-tions, of profiting by experience, of experimenting in novelsituations, and so on. Association.—It was a great step in evolution whenanimals began to associate sensations together. We meanby a sensation, physiologically, an impression made on thenervous system by external stimulus, and psychologically,an awareness (to some degree) of the external us refer briefly to some of the experimental work whichhas been done in the study of the association of is, for instance, the work of Pavlov and his schoolon the establishment of associations in the dog. It is wellknown that a dogs mouth may water when it sees food;there is a reflex stimulation of the salivary glands, notby direct contact with food, but cirouitously by a visualimpression. When the food is put in the dogs mouth,the salivation must follow; when the stimulation is cir- Fig. 44.—Bird-catc|iiiifg spider , ;(Mygale avicularia) catchinghumniing>^DiTrd, •: From a THE WAYS OF LIFE 243 cuitous the result is inconstant. Pavlov showed that ifa whistle is always sounded when a dog gets somethingto eat, then by and by the sound of the whistle will makethe dog salivate. An association between the sound andthe gustatory excitation has been estabhshed. The stimulus that suggests the sahvation may bealmost anything if the dog has the association estab-lished—^it may be, besides sight and sound, an odour, amovement, a change of temperature or illumination, ascratching of the skin, and so on. The method is usefulin definitely proving the animals sensitiveness to variousstimuli—some of them well known to all who know dogs,and others a httle surprising—^but its chief value is inshowing the establishment of cerebral associations, and indiscovering their laws. The experiments leave in the minda vivid impression of the remarkable plasticity of the dogsbrain in forming associations. Thus, Orbeli succeeded inestabhshing a reflex betw
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