# Sensing Performance of a Vibrotactile Glove for Deaf-Blind People
## 4 Discussion  
In order to represent a wide range of population, the CS were selected on a gender-balance basis and age interval from 18 to 58 years old. Older age was limited to avoid tactile sensitivity decrease that comes with age [24]. The CS are younger adults attending to mean age value, so a better sensitivity is expected from them. This makes the comparative test more challenging for the DBS. Compared to the CS, the DBS had a better performance. This was not totally unexpected as gathered in the corresponding scientific literature: people with some kind of sense impairment often achieve better acuity through another sense (for example, touch) [31; 44]. Therefore, future studies on vibrotactile recognition can be carried out by focusing on the performance and the learning of unimpaired subjects. This is due to the fact that most DBS develop better touch sensitivity than unimpaired people; notwithstanding, it is convenient to ensure the validity of the vibrotactile analyses with unimpaired individuals. This will allow us to increase the population sample, make face-to-face tests, and minimize communication issues. However, the tests also need to be performed on DBS  
Figure 7: Finger success rate for each of the three recognition attempts carried out by the DBS. In the polar diagram, the similarity in performance for each of the fingers is noticeable. because we cannot disregard their feedback, as they are the potential users. They should also participate in the system development sequence [32]. Pattern recognition improves with the activation of a single tactor. Therefore, the codification of stimuli with a single tactor can be prioritized so as to associate them with the most important concepts or ideas. Thus, two keying frequencies applied to the five fingers give 10 stimuli combinations. This number of combinations is deemed to be good enough to communicate the most important everyday concepts for the interaction between DBS and their care-givers. This is a significant advance for those DBS with no knowledge of adapted language or for those who already handle one but do not require a large number of concepts. The number of orders with a single tactor can be increased by adding a third keying frequency. This new frequency could be either (a) in the range from 1 Hz to 10 Hz that meets the aforementioned timing constraints [20], such as 5 Hz, or (b) a 0 Hz keying, i.e., a 170 Hz stimulus burst with no interruption. These keying frequencies can be adapted to each user by choosing a custom set aimed at achieving the best performance. Hence, the new frequency expands the stimulation pattern set and maintains the two-dimensional mapping, i.e., tactor activation and tactor keying frequency. This expanded map fits with the span of absolute judgment and the span of immediate memory [37]. Thus, the inclusion of a new dimension that could decrease the users' performance is avoided [38]. When the stimulation pattern set is expanded by increasing the keying frequencies, those frequencies that meet the timing constraints improve recognition. The experiments show a similar detection performance for both 1 Hz and 10 Hz and their combination. However, the increase in the keying frequency can introduce the skin effect. This effect integrates specific spatio-temporal stimuli, so spatial and temporal masking can be produced [20]. Thus, timing constraints should be met in order to achieve a balanced recognition performance among the keying frequencies as well as a high success rate. Great recognition efficiency can be achieved by stimulating the fingers. According to classical studies, as explained in the introduction section, the fingers are one of the most sensitive parts of the body. The developed system takes advantage of these features by means of the vibrotactile stimulation of the five fingers of the right hand. This technique raises a problem because, although the HMI glove allows for the performance of all or almost all regular daily tasks, it is not comfortable for continuous use.