# Usability and Acceptance Analysis of Wearable BCI Devices
## 5 Results
### Questionnaire Results  
In order to evaluate two different EEG devices in terms of system, usability, and user acceptability, the (i) UHB headset device and the (ii) Diadem crown device, used to monitor the cognitive state of users during assembly activities with collaborative robots, were compared by means of point-in-time laboratory tests. Specifically, seven subjects (five males and two females) were evaluated, and while this experimentation aimed to deepen understanding of neural responses to specific stimuli during the execution of assembly tasks with a collaborative robot arm, it also provided a clear performance analysis of the systems. The experimental tasks were repeated with both devices on different days, and users were subsequently asked to evaluate the two devices based on the parameters identified by the state of the art. As Diadem has a rigid structure and, therefore, a fixed sensor arrangement, the electrode arrangement for UHB was designed to mirror as closely as possible the same configuration as Diadem so that the same pressure points were stimulated (see Figure 4). The sensors for Diadem are 14, Fp1, Fp2, F3, F4, F7, F8, P3, P4, P7, P8, O1, and O2, and the feedback sensor is a clip sensor that is required to be placed on the left lobe. For UHB, the sensors are 8, Fp1, Fp2, F3, F4, P3, P4, O1, and O2, and the feedback sensors are two ECG adhesive clips placed on the mastoid bone on either side of the neck. The dry electrodes' shape must (a) permit passage through the hair layer, (b) make dependable contact with the scalp, (c) adjust to the curve of each individual's skull, and (d) distribute pressure uniformly while avoiding excessive local pressure points [52]. The UHB device, although elastic, has hybrid sensors--both dry and saline--with conductive rubber large enough to touch the scalp and easily pass through the hair. The Diadem device, on the other hand, has short and slightly pointed dry sensors, so a lot of pressure had to be applied to touch the scalp, which caused a sense of discomfort. The so-called \"flower electrode\" on the UHB has a larger contact area with the scalp and is more adaptable to the shape of each head because of its size, shape, angle, and pin arrangement. When  
Figure 4: Distribution of device sensors, according to the International 10/20 System. the electrode is pressed against a surface, its design expands the contact area between the electrode and the scalp and restores mechanical stability [52]. The contact area is increased when the electrode is placed on the head because the electrode pins bend in contact with the scalp after passing through the hair. Expanding the contact area enhances comfort in addition to the electrical connection. Questionnaire results show that the elastic headset device is preferred, albeit slightly, in terms of comfort, whereas in terms of formal acceptability, all users showed a strong preference for the Diadem device (see Figure 5). In particular, there was a clear difference between male and female subjects: male users preferred the Diadem device in terms of comfort, reporting that it was less painful, and female users reported that the UHB device adapted better to the shape of the head, allowing contact between the sensors and the scalp through the hair without too much pressure (despite the larger size of the electrode), improving overall comfort. These considerations are also supported by the less deep and less visible skin marks of the flower electrodes in most subjects. These considerations are in line with the study by [PERSON] et al. [23], whose results indicate that women are less sensitive than men (higher PDT) in terms of absolute PDT values, especially on the scalp, and who hypothesizes that this is due to the hair, which can dampen and diffuse the applied pressure. As an example, the results suggest that hair density could decrease vibration sensitivity in less sensitive parts of the head and marginally block vibration signals from reaching the scalp [53].