# Usability and Acceptance Analysis of Wearable BCI Devices
## 4 Wearable Neuroimaging Devices Usability Factor Identification
Furthermore, two devices, specifically Unicorn Hybrid Black (UHB) and Diadem, are investigated during laboratory assembly activities with a collaborative robot. A self-assessment questionnaire of system usability and acceptability is administered to the sample of users for each device used. These studies show that caps with gel-based electrodes induced general discomfort, although they remain the most popular option in terms of adapting to changes in shape and head size. In addition to signal quality issues, there are difficulties with the fit of the cap in terms of the adaptability of the devices to different head sizes, comfort, and preference of the device by subjects [30; 35]. Therefore, for the evaluation of an EEG/fNIRS device from the perspective of system and user usability and acceptability, the two device configurations, i.e., caps and crowns, were compared. The following aspects were identified for the evaluation:  
1. **Adaptability and fit**: the caps generally have a mechanism to adapt to the shape and size of the head, unlike crowns, which, being configured with rigid or semi-rigid structures, do not always manage to adapt to different head conformations;
2. **Comfort:** the caps, which are usually made of elastic and lightweight fabric, have a greater ability to adapt to the user, improving perceived comfort. Conversely, the rigid or semi-rigid configuration of the crowns may cause discomfort due to the lack of adaptability to the head, resulting in a feeling of instability and a more uneven weight distribution;3. **Wearability (ability of the device to be worn):** crowns are usually quicker to put on than caps, which may require assistance, especially when supplemented with wet gel electrodes. In addition, crowns allow for one-handed use, which is essential for users with disabilities or operators in work contexts;
4. **Formal acceptability**: the configuration of crown devices is defined to have a small footprint and a desirable appearance in terms of aesthetics. In contrast, caps are often configured with a wiring system that is less practical and formally cumbersome;
5. **Electrode setting:** caps have guiding elements applied to the fabric, which allows correct positioning of the electrodes, according to the international standard 10-20. In contrast, crowns may cause electrode displacements in different sensing sessions and with respect to different configurations of the user's head;
6. **Data quality:** caps, unlike crowns, can help maintain the correct positioning of the electrodes on the scalp, decreasing noise and disturbance due to small vibrations and/or movements. This ensures a better resolution of the data for their synthesis and interpretation;
7. **Interoperability:** the devices, regardless of their cap or crown configuration, can be integrated with other technologies. To ensure this, it is essential that the device can communicate with non-device software and allow direct access to data;
8. **Ease of cleaning and disinfection:** caps are configured to be disinfected by surface cleaning, whereas crowns require immersion in a disinfection solution for several minutes following removal of the electrodes. However, this also differs depending on the type of electrodes the device is equipped with (dry, semi-dry, and salt-based).