Stroop Task

The Stroop task in the pre- and posttest was the version reported by Badin et al. (2016) and Gantois et al. (2020). The MF-inducing task in session 3 was a continuous Stroop task lasting 20 min (Stroop-20). Players were instructed to sit on the bench at the corner of the court and to hold the tablet (iPad, Apple Inc., California, United States) to perform the Stroop task individually under the supervision of one examiner. Players were provided noise-canceling headphones to minimize distractions. Gestures were only given for indicating the start and end of the task. Stroop tasks were programmed by E-Prime (Psychology Software Tools, PA, United States) and carried out on a full-HD screen (2,732 × 2,048 pixels, 12.9 inch) tablet; the virtual keyboard of the tablet was used for key pressing.

Colored words (red, blue, green, and yellow) were presented one at a time on the screen with a black background. Trials were arranged in a pseudorandom order with 50% of them being congruent (matched word and color) and 50% being incongruent, with all incongruent word–color combinations occurring with equal frequency. Players were required to respond to each trial by pressing one of the four keys on the bottom edge of the screen and then to choose the color of the word rather than its meaning. However, to increase task difficulty, if the word was displayed on screen in the color of red, the correct response was to press the key corresponding to the meaning of the word (Badin et al., 2016). The stimulus did not fade from the screen until a response was given. When the answer was correct, the stimulus disappeared, and a new one was set immediately, while any incorrect answer elicited a beep sound to prompt more accurate performance and a new stimulus subsequently appeared (Gantois et al., 2020). Moreover, to prevent the subjective slack during the task, we established the cutoff value of mean response time at 1.5 s, any slower data (<800 trials) were excluded for analysis. Players were motivated to perform faster than the cutoff value by the provision of an additional ¥50 RMB reward.

In the pre- and posttest, the 3-min short version of the Stroop task (Stroop-3) was used to assess the cognitive performance, with the measures of response time and response accuracy. Stroop-3 followed all the rules as Stroop-20, during which the player was asked to respond no less than 120 trials.