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Removing Timing Shortcuts Improves Non-Invasive Brain-to-Text (arxiv.org)
3 points by sbulaev 1 day ago | hide | past | pdf | discuss on HN

In plain words: Overlapping windows in brain-to-text decoding reveal each spoken word's length, so the network guesses words from timing alone; processing windows one at a time removes this shortcut. Once fixed, pooling repeated readings of a word and a language model's guesses cuts word error to 36.6%.

Abstract

We find that major reported improvements in decoding words from non-invasive brain recordings are largely reproducible without any brain data. In the influential work of d'Ascoli et al. (2025), time series of brain activity from subjects perceiving continuous speech are segmented into fixed-length windows starting at each word. A neural network then generates predictions for all of the words in a sentence together. Neighbouring windows partially overlap, implicitly revealing the interval between words. Since these intervals indicate the duration of the words spoken, and different words tend to have different durations - for example, "the" is much shorter than "supercalifragilisticexpialidocious" - the neural network can improve its predictions of words without relying on the underlying brain activity. Consistent with this, the method reaches 22.0% balanced accuracy on synthetic signals containing no brain information, compared with 22.3% on real brain recordings. To prevent the network from learning this shortcut, we make a single, simple change. Instead of jointly encoding all windows in a sentence, we process each independently. As a result, the neural network achieves better performance by learning underlying word-specific information from brain recordings. This makes two existing strategies become much more effective than before. Both aggregating predictions from distinct neural responses to the same word and using a pretrained LLM as a linguistic prior now substantially improve results. On our perceived speech benchmark, this simple recipe (SimpleB2T) achieves a word error rate of 36.6% with five observations per word, approaching past invasive speech decoding performance, albeit under different conditions. The results in this work expose an important shortcut in brain-to-text decoding and show that removing it leads to a simple and considerably more effective strategy.

Dulhan Jayalath, Oiwi Parker Jones
arXiv:2609.40359 · cs.LG, q-bio.NC · submitted Sep 30, 2026
abstract · pdf · html · 29 pages, 12 figures, 10 tables

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