Abstract: Many studies suggested the establishment of sentence meaning in sentence comprehension was based on lexical integration, which reflected on N400 starting around 250ms after the onset of an incoming word. However, research related to the semantic P600 effect proposed that there might be other route (s) for meaning establishment besides lexical integration, which might start earlier than the onset of the processing reflected on N400. Here four experiments were conducted to investigate whether there are other route (s) earlier than the processing indexed by N400 and when they begin.
In Experiment 1, a paradigm related to Perceptual Symbol Theory (PST) was used for study. Participants were asked to read Chinese sentences like 天空中有一只老鹰 (In the sky there is an eagle) word by word, and then to judge whether the pictured objects that followed without interval had been mentioned in the preceding sentences ignoring their shape and state. The reaction times for judgment were recorded. The last word of each sentence which was a two-character word was the critical word. All critical words were presented in three different time durations: 550ms, 250ms and 200ms. According to previous studies and PST, when the critical word was presented at 550ms, participants could have established the sentence meaning and a mismatch effect would appear. The mismatch effect is an effect that the reaction time is shorter when the sentence matches the following picture. The result found that mismatch effect also appeared in both 250ms and 200ms durations, and their reaction times were similar to those of 550ms duration. The result suggested that participants could establish sentence meaning even when the critical word was presented at 200ms, which indicated that sentence meaning establishment started before the onset of N400.
Experiments 2 and 3 aimed at revealing a more precise time point at which readers began to relate the last word of a sentence to the preceding linguistic input and establish sentence meaning. The experimental methods were the same to that of Experiment 1 except for shortening the duration of the critical word. The results suggested that participants began to establish sentence meaning after the critical word was presented at 150ms.
Experiment 4 was conducted to counter some possible explanations for the experimental effects of Experiment 1~3. Doubters might think that the mismatch effects in Experiments 1~3 came from prime effect but not sentence meaning establishment. That is, the first word might prime the processing of the critical word or/and the following picture in the match condition. Experiment 4a was conducted to deal with this challenge. Participants were presented with Chinese word pairs like 天空－老鹰 (sky-eagle), and then asked to complete a judgment task as in Experiments 1~3. All word pairs were constructed based on Experiments 1~3 by combining the first word and critical word of each sentence. The results showed that the mismatch effect did not appear in Experiment 2, which supported the findings of Experiments 1~3. One might also doubt whether readers could establish sentence meaning in the short critical word present time conditions, like 150ms and 200ms, and think that the reason for the appearance of the mismatch effects was that the sentential context facilitated the access or selection of the critical word’s perceptual symbol which was consistent with it. In Experiment 4b, participants were asked to complete experimental tasks similar to Experiments 1~3. Unlike Experiments 1~3, sentences were reconstructed, the critical words were moved away from the sentence end, and the last words were present at 150ms or 200ms. The results showed that in both the duration conditions, mismatch effect was present, which also supported Experiments 1~3.
In conclusion, the results suggested that during sentence comprehension, readers could relate an incoming two-character Chinese sentence-end word to the preceding linguistic input about 150ms after its presentation and establish the sentence meaning, and sentence meaning establishment started before the onset of the processing reflected on N400.

Key words: sentence comprehension, sentence meaning establishment, temporal feature, N400