Stage 2: During Conditioning:
During this stage a stimulus which produces no response (i.e. neutral) is associated with the unconditioned stimulus at which point it now becomes known as the conditioned stimulus (CS).
Often during this stage the UCS must be associated with the CS on a number of occasions, or trials, for learning to take place. However, one trail learning can happen on certain occasions when it is not necessary for an association to be strengthened over time (such as being sick after food poisoning or drinking too much alcohol).
Stage 3: After Conditioning:
Now the conditioned stimulus (CS) has been associated with the unconditioned stimulus (UCS) to create a new conditioned response (CR).