A reflex is an automatic response to a stimulus. Humans use reflex actions in only some of their behaviour, for example controlling the eye's pupil size.

Conditioned reflexes.

A reflex response to a new stimulus can be learned.

A Russian scientist called Pavlov trained dogs to expect food whenever he rang a bell. The dogs eventually produced saliva when they heard the bell ring.

1. The dog salivates naturally when given food
2. Pavlov rings a bell every time the dog eats
3. After much repetition the dog salivates when the bell rings, even when there is no food.

This is an example of a conditioned reflex. The dogs were conditioned to salivate when the bell rang.

• The food is called a primary stimulus.
• The ringing bell is called a secondary stimulus.

Another example of conditioning is a goldfish expecting food when seeing a…