Jaycee Dugard, who was kept imprisoned for almost 20 years, was a perfect example of this. She was told that no one was looking for her, and in the absence of any competing information, had a hard time not believing it. But she DID think of her mother, quite often, and believed that she must be looking for her. She was kept, in fairly good condition, except for the sexual abuse and rape, of course, by the man and woman who took her. That must have been quite different from the horrible conditions in which these girls were kept, while also being physically and mentally abused.
Both cases (Dugard and this one) seem similar. Same with Smart and Hornbeck and countless others. They were controlled by their captors. All of the living situations/conditions seem horrid to me.
The ages of two of the girls at the time of their abduction was 14 and 16 (almost 17). The third was 20 at the time she was abducted. Not that these ages matter with respect to their abuse and mental stress.