Читать книгу The Behavior of Animals - Группа авторов - Страница 37

Stimulus summation introduces the phenomenon of supernormal stimulus, i.e., a stimulus that is more effective at eliciting a response than the stimulus for which it evolved. In studies using dummies, various examples show that exaggeration of a sign-stimulus leads to an extraordinary increase in its efficacy. The courting behavior of a male stickleback depends on the swollen abdomen of the pregnant female. When presented with two model females, one showing a normal swollen and the other a hyper-swollen abdomen, respectively, the male will choose the latter (Rowland 1989).

Another example concerns the egg-retrieval behavior of brooding greylag geese, Anser. After an egg rolls out of its nest, the goose extends its neck toward the egg and with its flat mandible slowly rolls it back toward the nest (Lorenz & Tinbergen 1938; cit. Tinbergen 1951). If the goose is offered a choice of eggs of different sizes placed outside the nest, the largest one will be preferred, even if it is twice the size of its own egg and thus difficult to handle. Egg retrieval by the brooding herring gull, Larus argentatus, has been studied in even more detail by Baerends and his colleagues (Baerends & Drent 1982). In hundreds of experiments carried out over many years, they showed that a green, speckled egg the size of a football was preferred over the gull’s own brown egg, which is the size of a large hen’s egg.

Humans, too, take advantage of exaggerated stimuli for various communicative purposes. Messages can be made appealing by stressing features. In cartoons, caricatures, and graphic icons certain cues are accentuated in order to abstract and emphasize the expression of a subject or an object. Women’s eyes and lips are underlined cosmetically in order to make the face attractive and distinctive from other faces.