"But he's now trying to challenge me mentally, the things he's saying, the way he's acting, this is out of character.
"So I have to reassess Parker. I don't get where he's got this lease of confidence, I just don't get it but I'm going to have to assess Parker because he's not going to trouble me physically, he's trying to get to me mentally.
"I have to keep my cool and not get involved in any trash talking."
The build up to the fight has included stunts by Parker's promoter Duco Events aimed at belittling Joshua, and Parker's "glass chin" suggestions.
In assessing the other main challengers, Joshua said big former champion Tyson Fury would be a very tough opponent if he got back in shape.
"I just think he's awkward in the mind and he's awkward in his style," Joshua said.
"Unpredictable. You just don't know. He doesn't have one significant style. He may move around the ring and try and steal the win, he may just jab the whole fight.
"I've seen him fight guys like John McDermott years ago where he would just try and fight with you, Steve Cunningham where he tries to fight with him and he's more vulnerable.
"So I don't know what style Fury will possess but he's good because he can mix it up, he's a man of many trades."
American Deontay Wilder had technical weaknesses he could exploit.
"His record proves he has a powerful punch, but his powerful punch doesn't come with an uppercut, it doesn't come with a peach left hook," said Joshua.
"It just comes with a straight right hand. So you eliminate one or two of his main weapons, you kind of chip the tree down with Wilder and I think he starts to lose his confidence."
