ABSTRACT
Sensitivity to certain types of experience changes throughout life. It is not surprising, then, that particular experiences should sometimes produce longterm effects on behavior more readily at certain stages of the life-cycle than at others. A classical example is imprinting in birds; a young duckling quickly learns to direct its filial behavior toward a particular moving object when it is exposed to that object within a period of time that starts soon after hatching and finishes some days later (Lorenz, 1935; see also Hoffman, this volume). Another good example is provided by the song-learning of many birds; details of the species-characteristic song are acquired by example only if the male Chaffinch has heard that song during an early period in its life (Thorpe, 1961). Similar examples occur in human development. Learning a language and, particularly, learning to articulate its distinctive sounds is much easier in childhood than in later life (Lenneberg, 1967; see also Snow, this volume). Such phenomena are clearly important for those interested in the study of behavioral development. However, they have been undervalued in recent years as a consequence of the wide-ranging attacks on the notion of continuity and connectedness in development and the suggestions that the effects of early experience are obliterated later in life (e.g., Clarke & Clarke, 1976; Kagan, 1984; see also Hinde & Bateson, 1984, for further discussion of the issue).
