Publications
カンファレンス (国際) 3-Key-Input: Exploring the Theoretical Minimum Keys for Text Entry
Naoki Kimura
2026 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP 2026)
2026.4.21
How far can we reduce the number of physical keys if we endow an ambiguous keyboard with modern language models? Fewer keys increase hardware design freedom in constrained settings such as assistive devices and mobile form factors. This paper systematically evaluates text entry systems using 2–5 physical keys combined with language-model-based disambiguation. On a 300-sentence English corpus (100 sentences each for Business, Conversational, and Technical), we compare key counts (2–5), letter-to-key mappings (layout-based, frequency-based, intentionally worst-case), and decoders (Trie-only, GPT-2 beam search, GPT-4o selection). We find that 3 keys plus GPT-4o achieves a character error rate (CER) of 9.46% and a word error rate (WER) of 12.20%, reducing CER by 59% relative to 2 keys (CER 23.3%). At 3 keys, the key-stream entropy is 1.54 bits per character. While increasing to 5 keys improves accuracy (CER 5.4%), the marginal gains diminish. Mapping choice has a small impact under standard designs (delta CER < 0.5 percentage points), and even an intentionally worst mapping degrades CER by only +0.5 percentage points. Technical sentences yield roughly twice the error rate of Business sentences. These results suggest that, in our evaluated offline setting under a strong language model prior, 3 keys are a practical minimum for general English.
Paper :
3-Key-Input: Exploring the Theoretical Minimum Keys for Text Entry
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