Subword Representations Successfully Decode Brain Responses to Morphologically Complex Written Words
: Hakala, Tero; Lindh-Knuutila, Tiina; Hulten, Annika; Lehtonen, Minna; Salmelin, Riitta
Publisher: MIT PRESS
: CAMBRIDGE
: 2024
: Neurobiology of language
: NEUROBIOLOGY OF LANGUAGE
: NEUROBIOL LANG
: 5
: 4
: 844
: 863
: 20
: 2641-4368
DOI: https://doi.org/10.1162/nol_a_00149
: https://doi.org/10.1162/nol_a_00149
: https://research.utu.fi/converis/portal/detail/Publication/458252538
This study extends the idea of decoding word-evoked brain activations using a corpus-semantic vector space to multimorphemic words in the agglutinative Finnish language. The corpus-semantic models are trained on word segments, and decoding is carried out with word vectors that are composed of these segments. We tested several alternative vector-space models using different segmentations: no segmentation (whole word), linguistic morphemes, statistical morphemes, random segmentation, and character-level 1-, 2- and 3-grams, and paired them with recorded MEG responses to multimorphemic words in a visual word recognition task. For all variants, the decoding accuracy exceeded the standard word-label permutation-based significance thresholds at 350-500 ms after stimulus onset. However, the critical segment-label permutation test revealed that only those segmentations that were morphologically aware reached significance in the brain decoding task. The results suggest that both whole-word forms and morphemes are represented in the brain and show that neural decoding using corpus-semantic word representations derived from compositional subword segments is applicable also for multimorphemic word forms. This is especially relevant for languages with complex morphology, because a large proportion of word forms are rare and it can be difficult to find statistically reliable surface representations for them in any large corpus.
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Riitta Salmelin, Academy of Finland (https://dx.doi.org/10.13039/501100002341), Award ID: LASTU, 256887. Riitta Salmelin, Academy of Finland (https://dx.doi.org/10.13039 /501100002341), Award ID: 255349. Riitta Salmelin, Academy of Finland (https://dx.doi.org /10.13039/501100002341), Award ID: 315553. Minna Lehtonen, Academy of Finland (https:// dx.doi.org/10.13039/501100002341), Award ID: 288880. Annika Hultén, Academy of Finland (https://dx.doi.org/10.13039/501100002341), Award ID: 287474. Tiina Lindh-Knuutila, Aalto Brain Center. Riitta Salmelin, Sigrid Juséliuksen Säätiö (https://dx.doi.org/10.13039 /501100006306). Riitta Salmelin, Academy of Finland, Award ID: 355407.
