Vibrotactile Alphabets: Time and Frequency Patterns to Encode Information

Although many tactual communication methods have been developed over the past decades, few of them have been widely adopted in everyday lives. In this paper, we investigate the ability to deliver text messages using patterns of vibrations. By manipulating the duration and frequency of vibrations, we designed two vibrotactile alphabets, i.e. 3F Vibraille and 2F Vibraille, along with their corresponding numbers and symbols. The main difference between 3F Vibraille and 2F Vibraille is the number of frequency levels utilised. Both alphabets were evaluated through human experiments in terms of training time, learning process and recognition accuracy of words and symbols. For both alphabets, the results demonstrated that participants were able to recognise words and symbols at an accuracy of over
$90\%$
after 6-8 hours of training. The main difference between the alphabets was that 3F Vibraille achieved a higher transmission rate while 2F Vibraille required less training time.