A Comparative Evaluation of Mechanical Vibration and Ultrasonic Vibration on Smartphones in Tactile Code Perception

To improve touchscreen accessibility, it has been proved efficient to integrate tactile feedback into touchscreen devices. Two typical techniques can be used to offer tactile feedback on smartphones, namely, mechanical vibration (MV) and ultrasonic vibration (UV). However, (a) whether MV and UV are equally perceived and evaluated on usability is unknown, and if not, (b) which technique/feedback provides better usability and satisfaction. In this study, a comparative user study was conducted to evaluate user performance on tactile codes perception generated by MV and UV techniques. 10 tactile codes were designed using the two techniques, and 16 sighted and 5 visually impaired people were invited to take part in a tactile code perception experiment. Tactile codes perception accuracy, response time, and satisfaction on the MV and UV were recorded during the experiment. The experimental results show that the user perception performance of MV was significantly better than UV for both sighted and visually impaired participants. Participants obtained an accuracy approximately 3% higher, with the response time at least 3 s faster, and user satisfaction significantly higher (6.1 vs. 4.6 on a 7-point Likert rating scale) when using MV. Both sighted and visually impaired participants assessed MV with a higher preference over UV. Our results suggest that MV fits better to applications that require precise tactile code perception, for which UV may not be as suitable due to its lower recognition efficiency.