Influence of Nonobvious Learning on the Development of the Approach Response in Chicks (Gallus gallus)

The role of prenatal auditory stimulations in the development of the postnatal approach response in young nidifugous birds is well known. However most of the studies in this area treat these stimulations as passive events. The purpose of this experimental series is to establish a link between prenatal stimulations and concomitant modifications of embryonic environment (warming and egg turning). Chicks were thus tested in a situation in which they could choose between two pure tones, one of which was or was not prenatally associated with these two stimuli. All chicks of the four groups used here were artificially incubated at the laboratory. After hatching, one-day-old subjects were placed three times a day for 3 days in a situation of choice between two pure tones (HFT = 1000 Hz or LFT = 500 Hz, of 200 ms duration played back every 3 seconds). The operant response (crossing over one of the two active zones in the experimental cage) allows the subject to hear either HFT or LFT. Number and duration of passings over each active zone were recorded. Results of the first control experiment showed that from the first test day naive chicks displayed a spontaneous preference for the low frequency pure tone. Another group of chicks was prenatally stimulated with HFT. This did not significantly affect the initial preference. In a third group, prenatal stimulations were repeatedly associated with modifications of the embryo's environment, i.e., warming and egg rotation. Results showed that the expression of the spontaneous preference for LFT was significantly delayed. The fourth group confirmed the specificity of this effect. The contribution of such nonobvious prenatal learning to the development of the approach response is discussed. RESUME: he role des stimulations auditives prenatales dans le developpement des reponses postnatales d'approche des jeunes nidifuges est bien connu. Mais d'une maniere generale, ces stimulations sont traitees comme des evenements purement passifs. Le but de ces experiences est done de tester la possibilite d'etablir un lien entre les stimulations prenatales et certaines modifications de I'environnement embryonnaire telles que le retournement et le rechauffement de I'oeuf Des poussins, incubes artificiellement au laboratoire, ont ete places individuellement, trois fois par jour durant trois jours, dans une situation experimentale leur offrant un choix entre deux sons purs (HFT = 1000 Hz ou LFT= 500 Hz, duree: 200 ms, rythme de presentation: 3 par sec). C'est le passage sur I'une ou I'autre des deux zones actives de la cage experimentale qui permet au sujet d'obtenir I'audition de ces sons. Le nombre et la duree des passages sur chacune des zones sont enregistres. Les resultats de I'experience controle montrent que des le premier jour des poussins "naifs" s'orientent spontanement vers le son de basse frequence. La stimulation prenatale avec HFT ne modifie pas de maniere significative Address correspondence to M. Delsaut, Laboratoire de Psychophysiologie, Bat. SN4, Universite de Lille I, F-59655 Villeneuve d'Ascq Cedex, France. © 1991 Human Sciences Press, Inc. 239 240 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY ce comportement. Chez un troisieme groupe de poussins, HFT a ete systematiquement associe avec le rechauffement et le retournement de I'embryon. Dans ces conditions, I'expression de la "preference" pour LFT est significativement retardee. Un quatrieme groupe confirme cet effet en excluant un eventuel effet parasite du necessaire refroidissement de I'oeuf avant son rechauffement. Ces resultats montrent done que I'association, au cours de la periode prenatale, de stimulations qui ne presentent pas de rapports evidents avec la reponse locomotrice postnatale, modifie cette reponse. La contribution d'un tel apprentissage au developpement de la reponse d'approche est discute. In young nidifugous birds, the audition of some maternal cries induces behavior such as that of approaching the sound source (maternal assembly call) or, on the contrary, freezing or withdrawal (maternal alarm call). This behavior appears at the appropriate time, just after hatching, is species-specific and appears without previous experience of the object to which the behavior is addressed. It thus seems to be spontaneous or instinctive. A lot of research has shown that, in fact, the development of such behavior is strongly dependant on prenatal audition of their own or sibling vocalizations (Blaich & Miller, 1988; Gottlieb, 1975a,b,c, 1981; Guyomarc'h, 1972, 1973, 1974a,b; Miller & Blaich, 1984). These studies pointed out the inadequacy of proposing hypotheses in terms of innate or learning mechanisms to explain the ontogeny of "instinctive" behavior and conversely the importance of more subtle forms of experience (Gottlieb, 1982; Miller, 1988; Miller & Blaich, 1984). In actual fact, prenatal auditory stimulation may act either through an effect on nervous maturation (Gottlieb, 1975c) or through familiarization with the frequency modulation of the maternal call (Guyomarc'h, 1972, 1973). However, this research showing the importance of these prenatal auditory stimulations on the development of behavior that otherwise may be considered spontaneous, treats these stimulations as passive events. Interactions between the embryo and its environment do exist before hatching. For example, Tuculescu and Griswold (1983) have shown that vocal interactions between the embryos and the hen take place during the prehatching period. In fact, maternal vocalizations are frequently produced at relevant times of the embryo's life (e.g., when the mother comes back to the nest or during postural changes (Guyomarc'h, 1974b). These vocalizations thus may be associated with some pertinent events such as warming or egg rotation that provide many stimulations and that are important and necessary to ensure correct embryo development. Such interactions taking place necessarily in the embryo's natural environment are generally not taken into account. They are even reduced or purposely suppressed to control experimental factors. The purpose of this study is to examine the effect of prenatal stimulation in an experimental context closer to that existing in natural conditions. In particular, these experiments have been designed to test effects of the association of embryo environmental modifi-