2.2.1. Stroop Test

In the Strop test, a stress condition in the participants is induced, by asking them to perform a series of similar cognitive tasks with an increasing level of difficulty and engagemen<sup>t</sup> [37]. In previous works, it has been demonstrated that the increasing engagemen<sup>t</sup> in such kinds of tests gives rise to a different level of stress in the participant [38] and as a consequence, a different sitting posture on the chair is taken [21].

The test used in this study is based on displaying some words on a screen that the participant has to read in a predefined period of time: in particular, the selected words are the name of a color (e.g., "blue", "red", "black", etc.) and have been displayed written in black and white in a first phase while in a colored form in a second phase of the test. To best achieve a variation of the cognitive engagemen<sup>t</sup> and to increase the level of stress induced in the task, the phases are planned in order to induce the Stroop effect: in the first phase of the test, the participant is instructed through written indications to read the words displayed on the screen, while in the second phase he/she is invited to read aloud the color of the word, regardless of the meaning of the word (this will be called PHA in the following). Then the combinations (color–meaning) in the successive phases are: the name and the color are matching (e.g., the word "blue" is displayed using a blue color, PHB in the following); and the name and the color are not matching (e.g., the word "blue" is displayed using a red color, PHC in the following). Different sets of words are displayed in sequence, giving a fixed time slot to the participant to complete the reading of each set. In PHB, the task is very easy since the color of the word corresponds to its meaning. In PHC, the task is more demanding, and the number of mistakes

made by the participant increases (e.g., not all words in the set are read or the meaning of the word is read instead of its color). This is mainly due to the time provided to the participants to complete the task being limited. Moreover, the participant is warned of the errors he/she made, and this induces a stressing condition that usually is maintained and growing till the end of the test.

In this work, a Stroop test consisting of 25 PowerPoint slides was realized and it was presented to a population of volunteers while sitting on the designed chair. In particular, according to the results obtained in [21], the test sequence (PHA, PHB, PHC) is described in the following and shown in Figure 5:



**Figure 5.** Black and white color words (**a**); matching color words (**b**); and non-matching color words (**c**) displayed respectively during phases PHA, PHB and PHC of the Stroop test.

Within each phase, the word set presented to the volunteers has an increasing number of words composing a slide that has been displayed in full screen mode. A fixed time delay for transition between consecutive sets has been set according to [21] to be able to induce the Stroop effect. Moreover, this choice allows for uniform test conditions for the whole population of participants, together with the standardization of the adopted font size (96 pt.) for all the displayed words.

The adopted settings are reported in Table 1.

**Table 1.** Schedule of the Stroop test—in the first phase the words are in black and white, in the second phase the color of words matches the word meaning, and in the third phase the color of words does not match the word meaning.

