According to analysis by Football Outsiders, the Cincinnati Bengals struggled mightily against play action in 2011. Seeing play action on 20% of all defensive snaps, the Bengals finished with the 4th worst play action defense per Football Outsiders DVOA rankings ("Defensive-adjusted Value Over Average", which is explained here), in front of only the Carolina Panthers, Minnesota Vikings and Denver Broncos.
It's difficult to pin the blame on any one section of the defense. Cornerback depth was certainly an issue for the Cincinnati Bengals towards the latter half of 2011. Injuries ravaged the secondary--including a devastating Achilles injury to star cornerback Leon Hall--and for several weeks it seemed as though the No. 2 cornerback position was being filled on a "Well, who's healthy?" basis. The play at the linebacker position left a lot to be desired as well, and their production must improve. And the defensive line...well, they were awesome. Let's not blame them.
We must also point at the fact that the Bengals have traditionally struggled with covering opposing tight ends. When a play action route is designed, they are often times designed with the tight end in mind. Not being able to cover this position effectively has been the Bengals Achilles heel for years.
Draft picks and the influx of free agent acquisitions were brought in to shore up the defense in 2012, and hopefully, improve against the play action.