CONCEPTS IN BIOLOGY

PART IV. EVOLUTION AND ECOLOGY

 

18. Evolutionary and Ecological Aspects of Behavior

 

18.4. Kinds of Learning

 

Scientists who study learning recognize that there are various kinds of learning: habituation, association, exploratory learning, imprinting, and insight.

 

Habituation

Habituation is a change in behavior in which an animal ignores an insignificant stimulus after repeated exposure to it. There are many examples of this kind of learning. Typically, wild animals flee from humans. Under many conditions, this is a valuable behavior. Wild animals that frequently encounter humans and never experience negative outcomes may learn to ignore humans. Many wild animals, such as the deer, elk, and bears in parks, have been habituated to the presence of humans and behave in a way that would be totally inappropriate in areas near the park where hunting is allowed (figure 18.5).

 

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FIGURE 18.5. Habituation

These elephants in a national park are habituated to the presence of vehicles containing tourists.

 

Similarly, loud noises usually startle humans and other animals. However, constant exposure to such sounds cause the individuals to ignore them. As a matter of fact, the sound may become so much a part of the environment that the stopping of the sound causes a response. Habituation is valuable because the animal does not waste time and energy responding to a stimulus that does not have a beneficial or negative impact on the animal. Animals that respond continually to inconsequential stimuli have less time to feed and may miss other, more important stimuli.

 

Association

Association occurs when an animal makes a connection between a stimulus and an outcome. Associating a particular outcome with a particular stimulus is important to survival, because it allows an animal to avoid danger or take advantage of a beneficial event. If association allows the animal to get more food, avoid predators, or protect its young more effectively, this kind of learning is advantageous to the species. The association of certain shapes, colors, odors, or sounds with danger is especially valuable. There are three common kinds of association: classical conditioning, operant (instrumental) conditioning, and observational learning (imitation).

 

Classical Conditioning

Classical conditioning occurs when an involuntary, natural, reflexive response to a natural stimulus is transferred from the natural stimulus to a new stimulus. The response provoked by the new stimulus is called a conditioned response. During the period when learning is taking place, the new stimulus is given before or at the same time as the normal stimulus.

A Russian physiologist, Ivan Pavlov (1849-1936), was investigating the physiology of digestion when he discovered that dogs can transfer a natural response to a new stimulus. He was studying the production of saliva by dogs and knew that a natural stimulus, such as the presence or smell of food, would cause the dogs to start salivating. Then, he rang a bell just before presenting them with food. After a training period, the dogs began to salivate when the bell was rung even though no food was presented. The natural response (salivating) was transferred from the natural stimulus (the smell or taste of food) to a new stimulus (the sound of a bell).

Animals can also be conditioned unintentionally. Many pets anticipate their mealtimes because their owners go through a certain set of behaviors, such as going to a cupboard or opening a can of pet food prior to putting food in a dish. It is doubtful that this kind of learning is common in wild animals, because it is hard to imagine such tightly controlled sets of stimuli in nature.

 

Operant (Instrumental) Conditioning

Operant (instrumental) conditioning also involves the association of a particular outcome with a specific stimulus, but it differs from classical conditioning in several ways. First, during operant conditioning, the animal learns to repeat acts that bring good results and avoid those that bring bad results.

Second, the animal receives a reward or punishment after engaging in a particular behavior. Third, the animal’s response is typically a more complicated behavior than a simple reflex. A reward that encourages a behavior is known as positive reinforcement, and a punishment that discourages a behavior is known as negative reinforcement.

The training of many kinds of animals involves this kind of conditioning. If a dog being led on a leash is given the command heel and is then vigorously jerked into the correct position, it eventually associates the word heel with assuming the correct position slightly behind and to the side of the trainer. This is negative reinforcement, because the animal avoids the unpleasantness of being jerked about if it assumes the correct position. Similarly, petting or giving food to a dog when it has done something correctly will positively reinforce the desired behavior. For example, placing the dog into the sitting position on the command sit and rewarding the dog when it performs the behavior on command is positive reinforcement.

Wild animals have many opportunities to learn through positive or negative reinforcement. As animals encounter the same stimulus repeatedly, there is an opportunity to associate the stimulus with a particular outcome. For example, many kinds of birds eat berries and other small fruits. If a distinctly colored berry has a good flavor, birds will return repeatedly to eat them. Pigeons in cities have learned to associate food with people in parks. They can even identify specific individuals who feed them regularly. Their behavior is reinforced by being fed. Many birds in urban areas have associated automobiles with food and are seen picking smashed insects from the grills and bumpers of cars. When a car drives into the area, birds immediately examine it for food.

In some national parks, bears have associated backpacks with food. In some cases, attempts have been made to use negative reinforcement to condition the bears to avoid humans. Usually, the bears are exposed to loud or painful stimuli if they approach backpacks. Some bears that cannot be trained to avoid humans and their “equipment” are killed. Conversely, in areas where bears are hunted, they have generally been conditioned to avoid contact with humans. Similarly, if certain kinds of fruits or insects have unpleasant tastes, animals learn to associate the bad tastes with the colors and shapes of the offending objects and avoid them in the future (figure 18.6). Each species of animal has a distinctive smell. If a deer or rabbit has several bad experiences with a predator that has a particular smell, it can avoid places where the smell of the predator is present.

 

 

 

Animals also engage in trial-and-error learning, which includes some elements of conditioning. When confronted with a problem, they try one option after another until they achieve a positive result. Once they have solved the problem, they can use the same solution repeatedly. For example, if a squirrel has a den in a hollow tree on one side of a stream and is attracted to a source of food on the other side, it may explore several routes to get across the stream. It may jump from a tree on one side of the stream to another on the opposite side. It may run across a log that spans the stream. It may wade a shallow portion of the stream. Once it has found a good pathway, it is likely to use the same pathway repeatedly. Similarly, many hummingbirds visit many different flowers during the course of a day. When they have found a series of nectar-rich flowers, they follow a particular route and visit the same flowers several times a day.

 

Observational Learning (Imitation)

Observational learning (imitation) is a form of association; it consists of a complex set of associations formed while watching another animal being rewarded or punished after performing a particular behavior. The animal does not receive the reward or punishment itself but, rather, observes the positive outcomes of the other’s behavior. Subsequently, the observing animal may show behaviors that receive rewards and avoid behaviors that lead to punishment. It is likely that conditioning is involved in imitation, because an animal that imitates a beneficial behavior is rewarded. Observing a negative outcome to another animal is also beneficial, because it allows the observer to avoid negative consequences. Many kinds of young birds and mammals follow their parents and sample the same kinds of foods their parents eat (figure 18.7). If the foods taste good, they are positively reinforced. They may also observe warning and avoidance behaviors associated with particular predators and mimic these behaviors when the predators are present. For example, crows will mob predators, such as hawks and owls. As young crows observe older ones cawing loudly and chasing an owl, they learn the same behavior. They associate a certain kind of behavior (mobbing) with a certain kind of stimulus (owl or hawk).

 

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FIGURE 18.7. Observational Learning

By following and observing their mother, these cubs will learn how to fish for salmon.

 

Exploratory Learning

Animals are constantly moving about and sampling their environment. For animals that rely primarily on instinctive behaviors, this movement increases the likelihood that they will find food or other valuable resources but does not result in learning because they do not increase their efficiency at finding resources. Animals that have a significant amount of memory can store information about their surroundings as they wander about. In some cases, the new information may have immediate value—for example, many kinds of birds and mammals remember where certain physical features are located in their environment. They may find a food source during their wanderings and can return to it repeatedly in the future.

When you put up a bird feeder, it does not take very long before many birds are visiting the feeder on a regular basis (figure 18.8). Birds certainly find suitable nesting sites by exploring; then, they store the location in memory. Even invertebrate animals with limited ability to store information engage in exploratory learning. For example, in spring, a queen bumblebee will fly about, examining holes in the ground. Eventually, she will find a hole in which she will lay eggs and begin to raise her first brood of young. Once she has selected a site, she must learn to recognize that spot so that she can return to it each time she leaves to find food, or her young will die.

 

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FIGURE 18.8. Exploratory Learning

As a result of traveling about, these goldfinches located this bird feeder. Once they found this food source, they could return repeatedly to obtain food.

 

In other cases, the information learned is not used immediately but might be of use in the future. If an animal has an inventory of its environment, it can call on the inventory to solve problems later in life. Many kinds of animals hide food items when food is plentiful and are able to find them later when food is scarce. Even if they don’t remember exactly where the food is hidden, if they always hide food in a particular kind of place, they are likely to find it later. (For example, if you needed to drive a car that you have never seen before, you would know that you need to use a key, and you would search in a particular place in the car to insert the key.) Having a general knowledge of its environment is very useful to an animal.

Many kinds of small mammals, such as mice and ground squirrels, avoid predators by scurrying under logs or other objects or into holes in the ground. Experiments with mice and owl predators show that mice that are familiar with their surroundings are more likely to escape predators than are those that are not.

 

Imprinting

Imprinting is a special kind of irreversible learning in which a very young animal is genetically primed to learn a specific behavior in a very short period during a specific time in its life. The time during which imprinting is possible is known as the critical period. This type of learning was originally recognized by Konrad Lorenz (1903-1989) in his experiments with geese and ducks. He determined that, shortly after hatching, goslings and ducklings would follow an object if the object was fairly large, moved, and made noise. The critical period was short—minutes to hours immediately following hatching.

Imprinting is irreversible. Ducklings will follow only the object on which they are originally imprinted. Under normal conditions, the first large, noisy, moving object newly hatched ducklings see is their mother. Imprinting ensures that the immature birds will follow her and may learn appropriate feeding, defensive tactics, and other behaviors by example. Because they are always near their mother, she can also protect them from enemies or bad weather. If animals imprint on the wrong objects, they are not likely to survive (figure 18.9a).

 

 

FIGURE 18.9. Imprinting

Imprinting is irreversible learning that occurs during a very specific part of the life of an animal. (a) Ducklings exhibit the “following response” to their mother. (b) Female sheep imprint on the odor of their lambs and will only let their lambs nurse.

 

Since these experiments by Lorenz in the early 1930s, scientists have discovered that many young animals can be imprinted on several types of stimuli and that there are responses other than following. The way song sparrows learn their song appears to be a kind of imprinting. The young birds must hear the correct song during a specific part of their youth, or they will never be able to perform the song correctly as adults. This is true even if later in life they are surrounded by other adult song sparrows that are singing the correct song. Furthermore, the period of time when they learn the song is before they begin singing. Recognizing and performing the correct song is important, because it has a particular meaning to other song sparrows. For males, it conveys that a male song sparrow has reserved a space for himself. For females, the male’s song is an announcement of the location of a male of the correct species that is a possible mate.

Mother sheep and many other kinds of mammals imprint on the odor of their offspring. They are able to identify their offspring among a group of lambs and allow only their own lambs to suck milk (figure 18.9b). Shepherds have known for centuries that they can sometimes get a mother that has lost her lambs to accept an orphan lamb if they place the skin of the mother’s dead lamb over the orphan.

Many fish appear to imprint on odors in the water. Salmon are famous for their ability to return to the freshwater streams where they were hatched. Fish that are raised in artificial hatcheries can be imprinted on minute amounts of specific chemicals and be induced to return to any stream that contains the chemical.

 

Insight

Insight is learning in which past experiences are reorganized to solve new problems. When faced with a new problem, whether it is a crossword puzzle, a math problem, or any other, everyday problem, we sort through our past experiences to find those that apply. We may not even realize we are doing it, but we put these past experiences together in a new way that may solve the current problem. Because this process is internal and can be demonstrated only through a response, it is very difficult to understand exactly what goes on when insight occurs. Behavioral scientists have explored this area for many years, but the study of insight is still in its infancy.

Insight is very difficult to study, because it is impossible to know for sure whether a novel solution to a problem is the result of thinking it through or simply an accident. For example, a small group of Japanese macaques (monkeys) was studied on an island. They were fed by simply dumping food, such as sweet potatoes or wheat, onto the beach. Eventually, one of the macaques discovered that she could get the sand off the sweet potato by washing it in a nearby stream. She also discovered that she could sort the wheat from the sand by putting the mixture into water because the wheat would float. Are these examples of insight? We will probably never know, but it is tempting to think so. In addition, in the colony of macaques, the others soon began to display the same behavior, probably imitating the female that had first made the discovery. Table 18.2 summarizes the characteristics and significance of each of the kinds of learning discussed here.

 

TABLE 18.2. Kinds of Learning

 

Kind of Learning

Defining Characteristic

Ecological Significance

Example

Habituation

An animal ignores a stimulus to which it is subjected continually.

An animal does not waste time or energy by responding to unimportant stimuli.

Wild animals raised in the presence of humans lose their fear of humans.

Association

An animal learns that a particular outcome is connected with a particular stimulus.

An animal can avoid danger or anticipate beneficial events by connecting a particular outcome with a specific stimulus when that stimulus is frequently tied to a particular outcome.

Many mammalian predators associate prey with high-pitched, squealing sounds.

Classical conditioning

A new stimulus is presented in combination with a natural stimulus. The animal transfers its response from the natural stimulus to the new stimulus.

Classical conditioning probably does not happen in natural settings.

Pets can anticipate when they will be fed, because their owners’ food-preparation behavior occurs shortly before food is presented.

Operant (instrumental) conditioning

An animal responds to a new stimulus. It is rewarded or punished following its response. Eventually, the animal associates the reward or punishment with the stimulus and responds appropriately to the stimulus.

Animals can avoid harmful situations that are associated with particular stimuli. They can learn to repeat behaviors that bring benefits.

Animals that associate a shape, color, smell, or sound with a predator can take refuge. Animals that associate a shape, color, smell, or sound with the presence of food will find food more readily.

Observational learning (imitation)

An animal imitates the behaviors of others.

The animal can acquire the knowledge of others by watching. This can be more rapid than learning by trial and error.

Young animals run when their mothers do and feed on the food their parents do.

Exploratory learning

An animal moves through and observes the elements of its environment.

Information stored in memory may be valuable later.

An awareness of hiding places can allow an animal to escape a predator.

Imprinting

An animal learns specific, predetermined activity at a specific time in life.

The animal quickly gains a completely developed behavior that has immediate value to its survival.

Many kinds of newborn animals follow their mothers.

Insight

An animal understands the connection between things it had no way of experiencing previously.

Information stored in an animal’s memory can be used to solve new problems.

The manufacture and use of tools by humans and some other primates suggests insight is involved.

 

18.4. CONCEPT REVIEW

8. Give an example of a conditioned response. Describe one that is not mentioned in this chapter.

9. How are classical conditioning and operant conditioning different?

10. What is imprinting, and what value does it have to an organism?

11. Give an example of habituation in a wild animal.

12. In what kinds of animals is observational learning common?

13. Why is insight difficult to demonstrate in animals?

14. Give an example of the value of exploratory learning.