From bottom of page 141 and top of 142:
"A lexical decision task was used to assess the activation and cognitive fluency of aggressive concepts. The task entailed quick classification of letter strings as words or nonwords."
From the first page, 139:
"Typical experimental paradigms for testing cognitive fluency compare one or more violent video games with one or more nonviolent video games with respect to their fostering aggressive solutions to word fragment completion tasks (Carnagey & Anderson, 2005) or their speeding up aggressive concepts in word pronunciation tasks (Anderson & Carnagey, 2009; Anderson & Dill, 2000) or lexical decision tasks (Glock & Kneer, 2009). For purposes of experimental control, the accessibility of aggressive concepts is often defined by the difference between reactions to aggressive and control target words or stimuli, with the nonaggressive control stimuli typically being neutral or negative but nonaggressive."