From the article: "In each experiment, 12 subjects (280 total; ages 21.7 ± 1.5 year)"
This would imply that each variable group was composed of 12 participants but overall there were 280 participants.
This would imply that each variable group was composed of 12 participants but overall there were 280 participants.
"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".