An Evaluation of Auditory Learning in Filial Imprinting
The characteristics of auditory learning in filial imprinting in precocial birds are reviewed. Numerous studies have demonstrated that the addition of an auditory stimulus improves following of a visual stimulus. This paper evaluates whether there is genuine auditory imprinting, i.e. the formation of a preference for an auditory stimulus as a result of exposure to it. Many studies lack important features such as a balanced experimental design or a retention interval, which makes it difficult to draw firm conclusions from their results. The majority of studies of early auditory learning have used a compound of a visual and an auditory stimulus during training. Presentation of a visual object during auditory training improves learning about sounds. The visual stimulus may act as a US for learning about sounds. Alternatively, presentation of a visual stimulus may increase attention or arousal and thereby improve learning about the sound. In a large number of studies visual stimulation during auditory exposure was provided by the presence of a hen or siblings. Relatively few studies using only auditory exposure have demonstrated significant auditory learning. Exposure to a sound before hatching can lead to a significant preference for that sound when tested after hatching. However, such preferences are generally weak and short-lived. In a number of species, a predisposition for species-specific calls has been demonstrated, that is already apparent before hatching. It is concluded that auditory stimuli play an important role in the formation of filial preferences, but that auditory imprinting is not as prominent as has sometimes been suggested, especially when compared to visual imprinting.