Effect of target size on non-visual text-entry

Touch-enabled devices have a growing variety of screen sizes; however, there is little knowledge on the effect of key size on non-visual text-entry performance. We conducted a user study with 12 blind participants to investigate how non-visual input performance varies with four QWERTY keyboard sizes (ranging from 15mm to 2.5mm). This paper presents an analysis of typing performance and touch behaviors discussing its implications for future research. Our findings show that there is an upper limit to the benefits of larger target sizes between 10mm and 15mm. Input speed decreases from 4.5 to 2.4 words per minute (WPM) for targets sizes below 10mm. The smallest size was deemed unusable by participants even though performance was in par with previous work.