Prediction is Production: The missing link between language production and comprehension.

Pedro_P

Abstract
Language comprehension  often involves the generation  of predictions. It has been  hypothesized that such  prediction-for-comprehension  entails actual language  production. Recent studies  provided evidence that the  production system is recruited  during language  comprehension, but the link  between production and  prediction during  comprehension remains  hypothetical. Here, we tested  this hypothesis by comparing  prediction during sentence  comprehension (primary task)  in participants having the  production system either  available or not (non-verbal  versus verbal secondary task).  In the primary task, sentences  containing an expected or  unexpected target  noun-phrase were presented  during  electroencephalography  recording. Prediction,  measured as the magnitude of  the N400 effect elicited by the  article (expected versus  unexpected), was hindered  only when the production  system was taxed during  sentence context reading. The  present study provides the  first direct evidence that the  availability of the speech  production system is  necessary for generating  lexical prediction during  sentence comprehension.  Furthermore, these important  results provide an explanation  for the recruitment of  language production during  comprehension.
Introduction
Recent studies have provided evidence for a potential role of production processes in language comprehension 1, 2, 3, 4, but what exactly is the link between production and comprehension is a central topic in language sciences and remains to be determined 5. Based on several recent frameworks, this missing link could be prediction. Listeners constantly predict upcoming information during language comprehension (to facilitate comprehension and dialogue), and such predictions are accompanied by covert production 6, 7, 8, 9. Except some indirect support in the literature showing that language production skills (category fluency task, production vocabulary) and prediction are related 10, 11, 12, 13, 14, there is no direct evidence so far that the production system is necessary for prediction during comprehension (see 15for review). Providing experimental evidence for this claim would generate important knowledge regarding the production-comprehension link and consequently improve our understanding of the neurocognitive foundations of human communication.
In the present study, we measured lexical prediction during sentence comprehension when taxing the production system. The rationale was that if production is mandatory for prediction, then prediction should vanish when the availability of the production system is reduced. This was done by preventing inner speech through articulatory suppression (AS; e.g., uttering a certain syllable repeatedly while completing the primary task 16). If performance on the primary verbal task relies on inner speech, it should be significantly impaired by AS because articulation of irrelevant information prevents subvocal rehearsal of the verbal input 17.
Lexical prediction can be measured through event-related potential (ERP) responses derived from electrophysiological recording during sentence reading. Importantly for our goals, there is consistent evidence that the mean amplitude of the N400 negative ERP component is sensitive to lexical predictability: The less predictable a word is, the more negative the ERP N400 component. For instance, reading “The king wore on his head…” leads to lexical prediction of the noun-phrase “a crown”. The sentence ending “a hat” elicits a larger N400 component on the noun (reflecting difficulty in unexpected target noun integration), and, importantly, a larger N400 component on the article (when expected and unexpected nouns are of different gender and thus preceded by differently gender-marked articles; “una corona”/a crown – “un sombrero”/a hat). Such ERP modulation (i.e., larger amplitude for ERP component elicited by the unexpected relative to expected article) has been repeatedly observed and interpreted as a marker of lexical prediction, by taking advantage of gender-marked determiners in Spanish 18, 19, 20, gender-inflected adjectives in Dutch 21and phonological properties of English (indefinite article “a” changed to “an” if the following noun begins with a vowel 22, 23but see 24for a lack of replication).
We compared three groups of participants reading highly constrained Spanish sentences containing expectedversusunexpected noun-phrases (primary task). Lexical prediction effects were measured through ERP N400 modulations on the article (whose gender was congruent or not with that of the most expected target noun) and compared across the three groups differing in the secondary task. To test whether taxing the production system would reduce lexical prediction, the SP (Syllable Production) group was assigned a verbal secondary task (i.e., AS) preventing participants from using their inner speech (pronouncing the syllable/ta/once on every word display). As a control for double-tasking, the TT (Tongue-tapping) group was assigned a non-verbal secondary task similar to AS but without requiring verbalization (tapping the tongue loudly once on every word). As a control for auditory feedback perception (inherently happening in the SP group), the SL group was assigned a ‘Syllable Listening’ secondary task (listening to own voice pronouncing/ta/on every word). If the production system is necessary to build up predictions, the N400 expectation effect elicited by the article should be reduced in the SP group relative to the control groups. As a control for proper sentence processing and lexical integration, we expected a significant N400 effect on critical nouns in the three groups.
Material and Methods
Participants
Sixty Spanish native speakers took part in the experiment. They were randomly assigned to three groups. The sample size was chosen based on previous ERP studies reporting N400 effects in sentence processing 19, 20, 23. Twenty participants (9 females; age range 19–30, mean: 25 ± 3) were assigned to the ‘Syllable Production’ (SP) group. Twenty participants were assigned to the ‘Tongue-tapping’ (TT) group. Two participants were removed from analyses because of large number of artefacts in electroencephalogram recording (more than 50% trials removed after artefact rejection). The final TT group consisted of 18 participants (11 females; age range 19–30, mean: 24 ± 3). Twenty participants were assigned to the ‘Syllable Listening’ (SL) group. For similar reasons than in the TT group, 2 participants had to be removed from analyses, the final TT group thus consisting of 18 participants (11 females; age range 19–30, mean: 23 ± 3). The three groups were matched on age (F[2,53] = 1.48, p = 0.24). All participants were right handed, their vision was normal or corrected to normal and they did not report any reading or neurological disorder. Participants all signed an informed consent form before taking part to the study that was approved by the BCBL ethics committee. The experiment was performed in accordance with relevant guidelines and regulations. They received a payment of 10€ per hour for their participation.
Materials
Stimuli consisted of 100 sentence contexts with two possible critical noun-phrases (article + noun): expected or unexpected (e.g., “El rey llevaba en la cabezauna corona/un sombreroantigua/antiguo” – “The king wore on his head an old crown[Fem]/hat[Masc]”; see Table  1for other examples of sentences). In 50 sentence contexts, the expected noun was masculine (“un/el + noun” expected noun-phrase) and the unexpected noun was feminine (“una/la + noun” unexpected noun-phrase). In the other 50 sentence contexts, the expected noun was feminine and the unexpected noun was masculine (all critical nouns were inanimate). The 200 sentences were divided into two lists of 100 and each participant was presented with one list (matched across groups). Sentence contexts and critical noun-phrases were used only once per list. Each list contained 50 expected and 50 unexpected noun-phrases. There were no semantic or syntactic violations as critical noun-phrases were always semantically and syntactically correct, albeit that one was more expected than the other (see Table  1). There were no gender violations such as in “la sombrero – the[Fem]hat[Masc]” or “el corona – the[Masc]crown[Fem]”. The target noun-phrase was never in sentence final position. Across sentences, the critical article was in position 13.1 (SD 3.7; range: 6–24) and followed by 2.2 (SD 1.1) extra words (range: 1–6).  (▪ ▪ ▪)

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