  Older adults increasingly adopt small-screen devices, but limited motor
dexterity hinders their ability to type effectively. While a 9-key (T9)
keyboard allocates larger space to each key, it is shared by multiple
consecutive letters. Consequently, users must interrupt their gestures when
typing consecutive letters, leading to inefficiencies and poor user experience.
Thus, we proposed a novel keyboard that leverages the currently unused key 1 to
duplicate letters from the previous key, allowing the entry of consecutive
letters without interruptions. A user study with 12 older adults showed that it
significantly outperformed the T9 with wiggle gesture in typing speed, KSPC,
insertion errors, and deletes per word while achieving comparable performance
as the conventional T9. Repeating the typing tasks with 12 young adults found
that the advantages of the novel T9 were consistent or enhanced. We also
provide error analysis and design considerations for improving gesture typing
on T9 for older adults.
