Singer. Hugh Laurie was credited as an executive producer for the second and third episodes of season five. Shore was Houses showrunner. Through the end of the sixth season, more than two dozen writers had contributed to the program. The most prolific were Kaplow (18 episodes), Blake (17), Shore (16), Friend (16), Lerner (16), Moran (14), and Egan (13). The show's most prolific directors through its first six seasons were Deran Sarafian (22 episodes), who was not involved in season six, and Greg Yaitanes (17). Of the more than three dozen other directors who have worked on the series, only David Straiton directed as many as 10 episodes through the sixth season. Hugh Laurie directed the 17th episode of season six, "Lockdown". Elan Soltes was the visual effects supervisor since the show began. Lisa Sanders, an assistant clinical professor of medicine at the Yale School of Medicine, was a technical advisor to the series. She writes the "Diagnosis" column that inspired Houses premise. According to Shore, "[T]hree different doctors ... check everything we do". Bobbin Bergstrom, a registered nurse, was the program's on-set medical adviser. Casting At first, the producers were looking for a "quintessentially American person" to play the role of House. Bryan Singer in particular felt there was no way he was going to hire a non-American actor for the role. At the time of the casting session, actor Hugh Laurie was in Namibia filming the movie Flight of the Phoenix. He assembled an audition tape in a hotel bathroom, the only place with enough light, and apologized for its appearance (which Singer compared to a "bin Laden video"). Laurie improvised, using an umbrella for a cane. Singer was very impressed by his performance and commented on how well the "American actor" was able to grasp the character. Singer was not aware that Laurie was English, due to his American accent. Laurie credits the accent to "a misspent youth [watching] too much TV and too many movies". Although locally better-known actors such as Denis Leary, David Cross, Rob Morrow, and Patrick Dempsey were considered for the part, Shore, Jacobs, and Attanasio were as impressed as Singer and cast Laurie as House. Laurie later revealed that he initially thought the show's central character was Dr. James Wilson. He assumed that House was a supporting part, due to the nature of the character, until he received the full script of