# Sensing Performance of a Vibrotactile Glove for Deaf-Blind People
## 2 Methods
### Apparatus  
The system allows the interaction between an unimpaired user A and a deaf-blind user B. User A does not need any previous knowledge of any adapted language, e.g., tactile sign language. The system design follows a methodology based on the involvement of all parties concerned [36]. This means that potential deaf-blind users, care-givers, and engineers collaborated closely in the discussion of trade-offs, achieving the implementation laid out here. The HMI consists of a glove that stimulates the fingers with a predefined pattern, as shown in Figure 2. Each finger has a tactor attached, i.e., a DC motor with an eccentric weight mounted on it, so there are five tactors. The DC motor is a CEBEK C6070, used as a vibrator in cellular phones. The  
Figure 1: Communication system: (i) smartphone as afferent human-machine interface (HMI) for the unimpaired interlocutor, (ii) stimulating glove as efferent HMI for the deaf-blind individual, and (iii) Bluetooth link. motors are controlled by an Arduino Micro board through a set of drivers to deliver the requested current. The Arduino board has a Bluetooth link to connect with the interlocutor. Tactor activation is coded with two on-off keying frequencies--1 Hz and 10 Hz--that modulate the activation or not of the actors, as shown in Figure 3. The transient time to achieve the full vibration is negligible at 10 Hz. And this starting transient is compensated with the stopping transient. Hence, a two-dimensional stimulus mapping is obtained, i.e., actor activation (location) and tactor keying frequency (rhythm). This mapping is consistent with the amount of information that can be received, processed, and remembered taking into account the span of absolute judgment and the span of immediate memory [37]. As previous studies have demonstrated, users perform better with two-dimensions rather than with three or more [38]. According to previous studies [39; 40], sensitivity towards the location of a touch or toward the separation between touched locations is greater when the body site is more mobile. Finger stimulation in this case fulfils this principle, and this was the main reason for choosing the glove as the efferent HMI. Thus, the fingers are used to stimulate the subject. On the other hand, it has been shown that repeated stimulation of a specific part of the body can lead to an improvement of tactile discrimination performance for that part of the body [41]. This allows the device to meet the user's wishes regarding the location of the HMI in another target body part. Hence, other possible HMI locations can be proposed, though proper training is required. The factor produces a stimulating burst generated by the 170 Hz factor rotation frequency. This stimulating frequency avoids the rapid adaptation to stationary touch stimuli [18]. The ratio between the applied amplitude and the achieved stimulus should be taken into account, as it is related to the tactor rotation frequency. The obtained 170 Hz is close to the range of frequencies with the lowest  
Figure 3: Applied signals to the actors: (**a**) the amplitude is an on-off keying at 1 Hz, and (**b**) the amplitude is on-off keyed at 10 Hz. These signals switch on the actors during the high level intervals. Thus, the shading indicates that the actor is vibrating. Figure 2: Efferent HMI developed for the vibrotactile stimulation of the subject. It consists of a glove with one tactor per finger. Each tactor is a direct current (DC) motor with an eccentric weight placed on the dorsal side of the finger, i.e., on the fingernail area. perception threshold amplitudes and, at that frequency, there is a sensitivity peak at the fingers that reinforces the effect [42]. This makes the HMI vibrotactile stimuli remain in conscious awareness. Hence, this set of characteristics match the requirements of the system.