Laura is conducting an experiment to study what the impact of noise level on subsequent aggressive behavior. In one condition, participants experience a loud, annoying squeaky noise
while trying to complete a task, and then are given a chance later to give another ostensible
participant a noise blast, too. In the other condition, the participants do not experience the
squeaky noise while trying to complete their task. After the study has been conducted, Laura
realizes that the loud room was lit more brightly than the quiet room. This difference in the
level of light is an example of a(n)