Q. How do you refer to the whole article and author in the introduction as to why you chose that article?

I don't know if we will find a rule on how to do this in the Publication Manual of the American Psychological Association, so I think we can just use a common sense rule. What does the reader need to know about the article? Probably these items -

• author
• title of the article
• year
• and maybe the journal title (this could be found using the reference list)

And since you are discussing why you chose the article, we can include these items in the text of your paragraph. Maybe something like this ...

"The 2015 winner of the John Beargrease Sled Dog Race Cutest Puppy Contest was an Australian Shepherd. Why does this breed always win and not, say, a Pug? Is it judicial bias? Or something else? It appears science might hold the answer. In his 2015 article "Human Selection of Desirable  Canine Traits," published in the Journal of How Dogs Manipulate Humans, author Todd White examines those canine characteristics that most appeal to humans. This article seemed to be the perfect starting point for my investigation into the potentially corrupt world of cutest puppy contests."

Obviously you might want to be less melodramatic and more scholarly in your paper, but I think this should work.