human

The call acts as an acoustic sign stimulus that directs the response of following. It is the physical act of following, however, that triggers the learning process; chicks passively transported behind a calling parent do not imprint at all. As long as the substitute parent makes the right sounds and moves, ducklings can be imprinted on a motley collection of objects, including rubber balls, shoe boxes, and human beings. This parental-imprinting phase is generally early and brief, often ending 36 hours after birth. Another round of imprinting usually takes place later; it serves to define the species image the animal will use to select an appropriate mate when it matures. Ethologists suspect that genetic programming cannot specify much visual detail; otherwise, selective advantage would probably require chicks to come prewired with a mental picture of their own species. As the world has become increasingly crowded with species, the role of sign stimuli in some animals has shifted from that of identifying each animal's species uniquely to that of simply directing the learning necessary to distinguish an animal's own kind from many similar creatures. This strategy works because, at the early age involved, most animals' ranges of contact are so limited that a mistake in identifying what to imprint on is highly unlikely. D2Characteristics of Programmed Learning Imprinting, therefore, has four basic qualities that distinguish it from ordinary learning: (1) A specific time, or critical period, exists when the learning must take place; (2) a specific context exists, usually defined by the presence of a sign stimulus; (3) the learning is often constrained in such a way that an animal remembers only a specific cue such as odor and ignores other conspicuous characteristics; and (4) no reward is necessary to ensure that the animal remembers.

These qualities are now becoming evident in many kinds of learning, and the value of such innately directed learning is beginning to be understood: In a world full of stimuli, it enables an animal to know what to learn and what to ignore. As though for the sake of economy, animals need pick up only the least amount of information that will suffice in a situation. For example, ducklings of one species seem able to learn the voices of their parents, whereas those of another recall only what their parents look like. When poisoned, rats remember only the taste and odor of the dangerous food, whereas quail recall only its color.