From the "Experiment Design" section of the paper, emphasis added: "The subjects were randomly divided into two groups. On the first day of the experiments, si

From the "Experiment Design" section of the paper, emphasis added: "The subjects were randomly divided into two groups. On the first day of the experiments, six subjects were sent to a forest site, and the other six subjects to a city site. On the second day, the subjects were sent to the other type of site as a cross-check." To me, that suggests 12 total subjects, and 280 "trials".