A level Biology exam revision resources written by A level Examiners





 

Learned behaviours develop during an animals lifetime, and are not passed on genetically to its offspring. They vary from very simple, to the complex social interactions in primates and whales. Learned behaviours can often be adapted - this adaptation of behaviour forms the basis of animal training.

The simplest learned behaviour is a modified reflex.

When a reflex is modified it is because the stimulus that causes the reflex also causes sensory information to be sent to the brain. When the learning has occurred this information causes inhibitory signals to be sent from the Central Nervous System (CNS) preventing the normal reflex response.

The most obvious example of this, is the control of the sphincters which govern urination and defaecation.

The reflex that empties the bladder is as follows. The full bladder is the stimulus which causes sphincter muscles around the base of the urethra to relax, these muscles are connected to the autonomic nervous system - to modify it this muscular relaxation has to be prevented which involves voluntary nerves exerting more control than before modification.

Learned Behaviour can be divided into different categories:

  • Habituation
  • Imprinting
  • Conditioning
    • classical conditioning
    • operant conditioning

Habituation is a reduction in a previously displayed response, when a stimulus is repeatedly applied with no reward or punishment following.

If you make an unusual sound near a cat, it will respond - usually by turning its head toward the sound. If the stimulus is given repeatedly, and nothing either pleasant or unpleasant happens to the cat, it will soon stop responding. This lack of response is long-lasting; when fully habituated, the cat will not respond to the sound even though weeks, or months, have passed since it was last made.

Another example, is the behaviour of some spiders that lie in wait for prey, to one side of their web, and when something gets trapped on the web, the spider detects the vibrations of the web and rushes out to kill its prey. This response can be made to occur, by simply tapping the web with a pen. However, after a few stimuli the spider stops responding. We say it has become habituated.

Young geese, if newly-hatched geese are exposed to a moving object of reasonable size, and emitting reasonable sounds, they will begin to follow it just as they would normally follow their mother.

This is called imprinting, (goslings) do not immediately recognise their mother but they imprint on her. There is a sensitive period, during the first few days of a goslings life, in which it will follow, and become attached to any large object, of course in nature this is the mother, but in some experiments it has been humans, or even in one study a red watering can. When goslings are distressed they will run to whatever object they have imprinted on, which usually will be advantageous, as it would be their mother, but not so helpful if the object was the red watering can.

In breeding programs, to replenish rare or endangered animals, care is taken to avoid imprint onto humans, and habituation to the presence of humans. In fact, habituation to human presence, is one of the factors that makes zoo and captive bred animals very different to their wild counterparts, and is an obstacle to reintroduction.

Conditioning involves the formation of new connections between stimuli and responses, the table below shows a summary of this


Type of Conditioning Summary

Classical A stimulus leads to a response. Here a new stimulus is given, at the same time as the first. After time the response occurs even if only the second stimulus is given.

Operant Trial and reward learning. A behaviour that occurs by chance, is reinforced, by providing a reward when the behaviour is performed.

The conditioned response is a simple form of learned behaviour. It is a response that - as a result of experience - comes to be caused by a stimulus, different from the one that originally triggered it. The Russian physiologist Ivan Pavlov found that placing meat powder in a dog's mouth caused it to salivate.

The placing of meat powder in the mouth of the dog is called the unconditioned stimulus (US) it is probably a simple inborn reflex, involving taste receptors, sensory neurons, networks of interneurons in the brain, and motor neurons running to the salivary glands.

Pavlov found that if he rang a bell every time he put the meat powder in the dog's mouth, the dog eventually salivated upon hearing the bell alone, without any meat powder present.

The dog has learned to respond to a substitute stimulus (the bell), this is known as the conditioned stimulus (CS).

We can assume that the physiological basis of the conditioned response is the transfer, by appropriate neurons, of nervous activity in the auditory areas of the brain, to the motor neurons controlling salivation. This involves the development of new circuits, which - we may also assume - is characteristic of all forms of learning.


Pre-Learning

unconditioned stimulus - (sight and smell of food)

unconditioned response - (salivation)


During Learning

unconditioned stimulus - (sight and smell of food)

conditioned stimulus - (bell)

unconditioned response - (salivation)


After Learning

conditioned stimulus - (bell)

conditioned response - (salivation)


We use the term "operant conditioning" to describe a type of learning that is also known as trial and reward learning. The classic experiments into operant conditioning were carried out by a psychologist called Skinner, where he trained rats and pigeons to press a lever in order to obtain a food reward (in a piece of apparatus which we call "skinners box"). In such experiments, the subject is able to generate certain motor-output responses (e.g. pressing a lever). The experimenter chooses a certain action (e.g. pressing the lever) to act as the response and to pair with an unconditioned stimulus (e.g. a food reward). After a training period, the subject will show the conditioned response (e.g. pressing the lever) if the response-unconditioned stimulus association has been memorized.



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