Muscle movements in teenagers' faces are being studied to establish if there is any link between violent video games and aggression.
The Massey University study is looking for any link between violent games and moral decision-making in children aged 13 or 14.
The study's author, master's student Sam Payne, attaches wires to the subjects' faces and records facial movements while they play.
Subjects also complete a moral-dilemma test, which Mr Payne said helped to determine how they were feeling after playing a violent game.
He said the survey would try to determine if a teenager made them angry or sad, or another emotion.
Many violent incidents, particularly in the United States - such as the mass shootings at Sandy Hook Elementary, Virginia Tech, and as far back as the Columbine High School massacre - have been linked by some social commentators to violent video games.