## 3 Materials and Method
### Data Collection and Protocol  
As depicted in Figure 3, the accelerometer sensor was meticulously affixed to a plastic holder and securely adhered in place through the judicious application of adhesive. Pertinent to the experimental configuration, certain parameters merit attention. Participants sat on a comfortable chair in front of a monitor. The participant's cranium was established at a distance of 80 cm. This interplay of measurements contributed to the precision and integrity of the experimental environment, offering a robust foundation for data acquisition and analysis. An expert set the correct position of the head and neck soon before starting each experimental session [45]. In the ensuing interlude, denoted as the second phase, the participant was granted a respite, affording them the freedom to move their head while remaining seated in the chair and permitting relaxation without specific posture constraints. The third phase (session 2) introduced visual feedback into the participants in the VF group. They were required to adopt an upright seated position, concomitantly positioning the sensor on their cranium while meticulously aligning their head in the prescribed orientation. Notably, the monitor was activated during this phase, ushering in real-time feedback. Data acquisition commenced under these monitored conditions, as delineated in Figure 3. It should be mentioned that for the participants in the control group there was no visual feedback, and the session was identical to session 1. The experimental protocol unfolded in a structured sequence comprising distinct phases. These procedural steps were meticulously designed to investigate the impact of visual feedback on posture maintenance. Each phase endured for a duration of two minutes, fostering comprehensive data acquisition and assessment. The inaugural phase, conducted without visual feedback, beckoned the participant to assume a proper seated posture. Ensuring precision, the sensor was affixed to the individual's cranium while meticulously anchored to its holder, nullifying any unintended displacement. The head assumed its ideal position, albeit slightly offset from the habitual stance, due to the presence of forward head syndrome. Subsequently, the participants were instructed to maintain this posture with the monitor deactivated, enabling discreet data recording. A subsequent intermission, designated as the fourth phase, allowed the participants to again enjoy a brief respite wherein they retained the liberty to move their head while maintaining a seated position. The fifth and final phase (Session 3), mirroring the initial phase but was conducted without visual feedback, compelling the participants to sit upright. The sensor iwas again situated on the cranium and with the head meticulously aligned. However, in this instance the monitor remained inactive, and data recording was resumed under these circumstances. It is worth noting that these test procedures were iteratively administered across ten sessions for each participant to ensure the robustness and reliability of the data collection process. For visual feedback, during the third phase of the experiment (Session 2), the experimenter orchestrated the alignment of the subject's head into an optimal orientation, with subsequent instructions to sustain this posture. Importantly, this phase entailed the activation of the monitor with visual display. The display featured a centrally positioned stationary blue circle alongside a dynamically mobile red circle representing the real-time tracking of the subject's head position. The subject was explicitly directed to superimpose the mobile red circle onto the stationary blue circle, thereby perpetuating a state of alignment between their head position and the designated reference point.