2. is the name of the scientist responsible for discovering the learning phenomenon known as conditioning, whereby an organism learns a response to a stimulus to which it normally would not respond.

The last three times little Theresa visited Dr. Lopez for checkups, he administered a painful preventive immunization shot that left her in tears. Today, when her mother takes her for another checkup, Theresa begins to sob as soon as she comes face to face with Dr. Lopez, even before he has had a chance to say hello.