International Journal of Comparative Psychology

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  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.