Testing Predictive Text Entry Methods with Constrained Keypad Designs

The problem of optimizing keypad designs for predictive text entry methods for handheld devices has received significant interest in recent years. The necessity of such optimization lies in the ever-increasing difficulty of inputting text into mobile devices, particularly those of extremely small size. Predictive keypad text entry methods, such as Tegic’s T9, only require one key press for each letter of a word to be entered. However, such methods are ambiguous since one key sequence may correspond to multiple matching words because more than one letter is mapped to each key. Various keypad designs have been proposed in the past to optimize the placement of letters on keys to minimize ambiguous key sequences. In contrast to past research that allowed mapping of any letters to any keys, we hypothesize that maintaining alphabetical ordering across the keys of optimized keypad designs will result in higher novice usability and ease of learning, while still providing a more immediate benefit in terms of improved performance. Results from usability testing we conducted are encouraging and support our hypothesis.