The woman in the wallpaper is John's wife's unconscious self-perception in regard to her current situation. In the end the situation of the wallpaper woman (and thus her own) consumes her. This consumption is concluded with her total loss of mind by the stories end.
This self-image is apparent in the common traits that develop between the narrator and the wallpaper woman. Since the wallpaper woman only exists in the narrator's eyes, only she can instill these traits into the trapped figure. When the narrator first sees the woman in the wall she is scared, she wishes, "...John would take (her) away from here." Soon the wallpaper woman begins to try to breakout from behind the pattern, paralleling her trying to escape John's "treatment". It becomes common that the narrator exhibits certain concerns and soon there after the wallpaper woman does something that parallels those concerns through an action.
Creeping is very important to this parallelism linking the two. At first the narrator sees the wallpaper woman creeping about outside. She exclaims that this behavior is odd for any woman, and it is apparent that it bothers her. Then only a few lines later the narrator states, "I always lock the door when I creep by daylight." thus admitting that she takes part in this odd activity too. Eventually all her movements about are creeping just as are the wallpaper woman's.
She finally gives into the wallpaper woman self-image fully; she rips down the wallpaper to free the woman/herself. "I pulled and she shook, I shook and she pulled" After this point the wallpaper woman exists no longer independent of her, she accepts that she is the wallpaper woman is her. She then talks as the woman trapped behind the wallpaper, "I wonder if they all come out of that wall-paper as I did?" and "I suppose I shall have to get back behind the pattern..." At last she escapes the torment by destroying the wallpaper. "I've got out at last, in spite of you and Jane." This statement explains the plight of the narrator; she is trapped in the wallpaper's barring pattern. The pattern represents John, Jane, and all those who keep her in the house. Her unconscious self-perception eventually overcomes her common sense and rules her life. The woman in the wallpaper starts as a self-perception and so becomes an alter ego. Eventually this alter ego overtakes her, and merges with her original self.