one at a time = one participant at a time?

Context:

For the study, the research team, which included Young Eun Huh, Tepper School of Business Ph.D. candidate, and Joachim Vosgerau, assistant professor of marketing, ran a series of five experiments that tested whether mentally stimulating the consumption of a food reduces its subsequent actual consumption. In the first experiment, participants imagined performing 33 repetitive actions, one at a time.