How the difference between a pond and

How do simple animals know what they need to accomplish? How do insects such as ants understand that they have to find food and bring it back to the nest? The answer: fixed action patterns.

What Is a Fixed Action Pattern?

Simply put, a fixed action pattern is a series or sequence of acts that occur behaviorally in animals. This sequence is unchangeable and will be carried out to completion once started, regardless of changes in the original stimulus. A stimulus is some external factor that will cause an organism to respond to it. Fixed action patterns are triggered by a type of external stimulus called a sign stimulus.

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The job of the sign stimulus is to start off the fixed action pattern of a particular organism.There are numerous examples of stimuli. One classic example is Pavlov’s dogs.

Pavlov trained his dogs to recognize that the sound of a ringing bell meant that they would receive dinner. Each time he fed them, he rang the bell. Eventually, he could ring the bell (the stimulus) and the dogs would begin to salivate (the response) because they believed that they were about to be fed. In a fixed action pattern, we see a similar occurrence, except there is a set sequence of actions that will occur in response to the stimulus. One other key difference between a fixed action pattern and the conditioning seen in Pavlov’s dogs is that the reaction in the fixed action pattern is innate rather than learned.

How Does It Work?

Put very simply, the sign stimulus occurs, and the organism responds to it. The response continues until the organism has completed whatever series of actions are in the fixed action pattern. It is a very simplistic response, one that occurs without the use of any real logic. It is not a behavioral response that is taught or learned; all fixed action responses are innate to the organisms that display them.Though still a hypothetical or theoretical idea at this time, scientists have proposed that there exists a neural network called the innate releasing mechanism that is responsible for all fixed action pattern behaviors in organisms. Other scientists studying behaviors in animals tend to disregard the idea of fixed action patterns, believing them too simple to capture what is really occurring.

Fixed Action Pattern Examples

Let’s look at some real examples of fixed action patterns in the animal world:1.

Some moths will fold their wings when they detect ultrasonic sounds from predators, such as bats. The moths fold up, drop to the ground, and hide in response to sensing the sounds. The sign stimulus is the ultrasonic sound, and the fixed action pattern is that they fold, drop, and hide.2. Mayflies, like many other insects, lay their eggs in standing pools of water such as ponds. The eggs remain moist, allowing them to grow and hatch, releasing the larvae which eventually become adults. Unfortunately, mayflies cannot discern the difference between a pond and a puddle on a road, so if they choose the latter, the puddle will dry up and kill the eggs.

In this example, the sign stimulus perceived by the mayfly is a particular way that light interacts with the surface of water and the fixed action pattern is that the mayfly lays its eggs in that body of water.3. Another classic and often cited example is the greylag goose’s egg rolling behavior. If a mother goose notices an egg has gotten pushed outside the nest, she will instinctively roll the egg back into the nest using a beak motion that occurs the same way every time. The goose will not stop this series of movements until the egg is back in the nest, even if the egg has rolled away again or an observer has taken the egg. The sign stimulus, therefore, is the egg being present outside the nest, and the fixed action pattern is the egg rolling behavior.

Fixed Action Patterns in Humans

There are very few perfect examples of fixed action patterns in humans, but a well-known one can be observed in infants. When presented with something to grab (a stick, some hair, or a finger for instance), infants will instinctively grip the object. Another example regularly occurring in humans is yawning. Often seeing someone yawn will trigger another person to yawn. Once a yawn has begun, it cannot be stopped until the behavior is completed.Many scientists would argue that as humans rely less and less on instinct for survival, our examples of fixed action patterns are decreasing. Culture, education, and technology have played large roles in how humans behave today; these factors are slowly changing our behavioral norms and innate responses to our environment.

Lesson Summary

A fixed action pattern is a sequence or series of actions that occurs as an organism’s response to a specific stimulus called a sign stimulus. A sign stimulus is any outside environmental interaction that elicits some response from an organism. Once a stimulus occurs, the organism engages in this particular sequence until completion – even if the circumstances that triggered the response change. It is not a logical reaction provoked by thought; it is simply a direct response to the stimulus. In some cases, such as moths, it is beneficial as they can hide from predators once they detect the ultrasonic sound produced by that predator. But in other cases, this behavior can be detrimental, such as mayflies laying eggs indiscriminately in any pool of water.


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