Fig. 2: Performance summary of the spelling system during the copy-typing task.

a Character error rates (CERs) observed during real-time sentence spelling with a language model (LM), denoted as ‘+LM (Real-time results)’, and offline simulations in which portions of the system were omitted. In the ‘Chance’ condition, sentences were created by replacing the outputs from the neural classifier with randomly generated letter probabilities without altering the remainder of the pipeline. In the ‘Only neural decoding’ condition, sentences were created by concatenating together the most likely character from each of the classifier’s predictions during a sentence trial (no whitespace characters were included). In the ‘+Vocab. constraints’ condition, the predicted letter probabilities from the neural classifier were used with a beam search that constrained the predicted character sequences to form words within the 1152-word vocabulary. The final condition ‘+ LM (Real-time results)’ incorporates language modeling. The sentences decoded with the full system in real time exhibited lower CERs than sentences decoded in the other conditions (***P < 0.0001, P-values provided in Table S2, two-sided Wilcoxon Rank-Sum test with 6-way Holm-Bonferroni correction). b Word error rates (WERs) for real-time results and corresponding offline omission simulations from A (***P < 0.0001, P-values provided in Table S3, two-sided Wilcoxon Rank-Sum test with 6-way Holm-Bonferroni correction). c The decoded characters per minute during real-time testing. d The decoded words per minute during real-time testing. In a–d, the distribution depicted in each boxplot was computed across n = 34 real-time blocks (in each block, the participant attempted to spell between 2 and 5 sentences), and each boxplot depicts the median as a center line, quartiles as bottom and top box edges, and the minimum and maximum values as whiskers (except for data points that are 1.5 times the interquartile range, which are individually plotted). e Number of excess characters in each decoded sentence. f Example sentence-spelling trials with decoded sentences from each non-chance condition. Incorrect letters are colored red. Superscripts 1 and 2 denote the correct target sentence for the two decoded sentences with errors. All other example sentences did not contain any errors. Data to recreate panels a–e are provided as a Source Data file.