He told Villa's website: "I grew up admiring Brad - he was definitely one of my heroes.
"What he has done in his tenure in the Premier League is unbelievable. And his new consecutive appearance record is phenomenal.
"Growing up as a young American goalkeeper and watching him in the 2002 World Cup in South Korea and Japan, which was a phenomenal competition for the USA, was an incredible feeling.
"He was very welcoming in helping me adapt to a new club, a new city and a new style of football.
"So for me, it was a great feeling to walk through the door and be treated so well. But it was even better to know that we both played in the same position and work together so closely.
"It is a healthy competition. We go in day in and day out and train together. It is a fantastic opportunity to learn from a great goalkeeper like Brad, who has done brilliantly domestically and internationally.
"It's an honour to work with him. Saying that, everyone wants to play and it's a hard situation being a goalkeeper because there's only one spot.
"My job is making it difficult for the manager when he has to make the decision at the end of the week.
"If I can do that, I have done my job. The rest is out of my hands."