Adapting Large Language Models for Character-based Augmentative and Alternative Communication
Dylan Gaines, Keith Vertanen
Stop building character-level models from scratch for AAC. Wrap existing subword LLMs with this conversion layer—you get better predictions without retraining. Best for AAC systems where users type one character at a time and need real-time suggestions.
AAC users typing letter-by-letter face a mismatch: state-of-the-art language models predict subword tokens, not characters. This creates a prediction gap that slows communication.
Method: The researchers built an algorithm that converts subword predictions from large language models into character-level predictions. Their method outperforms a classical character n-gram model by 9.4% in keystroke savings and beats a fine-tuned classification model by 2.8%. The key: they sample multiple subword continuations, extract character probabilities, and aggregate them—avoiding the computational cost of retraining models from scratch.
Caveats: Tested only on English text. Performance on languages with different morphology or writing systems is unknown.
Reflections: How does this approach perform on non-English languages with complex character systems? · Can the conversion algorithm be optimized for real-time mobile AAC devices with limited compute? · What's the user experience impact of the 2.8% keystroke savings in actual AAC usage?