To charlie overcome his phobia of heights, his therapist trains him to relax and then has him imagine climbing a ladder. after charlie visualizes climbing a ladder without anxiety, he attempts to imagine standing at the top of a tall building without feeling anxious. charlie's therapist is using a technique known as

systematic desensitization

Explanation:

systematic desensitization is psychological therapy to treat fear and phobias.It is based on principle of classical conditioning to reinforce a particular behavior, In this particular case it is used to overcome phobias. The steps involved in systematic desensitization is

1. Relaxation of muscles using deep breathing exercise

2.  step-wise Visualization of the fears

3. Exposing oneself to the fear and countering it

The process is repeated until the phobic person feels comfortable with his fear

answer; the sons of liberty;