Implicit Learning Of Artificial Phrase Structure Grammar

Language constitutes the foundation of human cognitive activities while grammatical rules are a key component of language. In the psychological research of language acquisition, a major focus is the acquisition of grammatical rules. A large number of studies have shown that individuals can generate new sentences according to grammatical rules even when they are infants, suggesting that the acquisition of grammar and language may be a subtle and implicit process. According to Chomsky hierarchy, grammar can be divided into 2 kinds:finite state grammar and phrase structure grammar. The latter is more important for language acquisition. However, most existing studies about implicit learning of grammar focused more on finite state grammar rather than the phrase structure grammar. Therefore, implicit learning of phrase structure grammar and its neural basis need further research and discussion.In view of this, the present research intended to bridge this gap by studies using carefully controlled conditions of implicit learning. The artificial phrase structure grammar on the carrier of Chinese tones was used. In addition, we controlled and manipulated the surface characteristics such as chunks in order to explore one basic theoretical question in the field of implicit learning. That is, what does individuals acquire through implicit learning? Rules or chunks?Four experiments were executed in the present study. Prior research indicated that phrase structure grammar on the carrier of Chinese tones could be implicitly learned by Chinese participants. However, the early experience was not controlled in previous studies. So it is hard to infer that phrase structure grammar could be implicitly learned generally. Therefore, in experiment 1, we explored whether the phrase structure grammar on the carrier of Chinese tones could be implicitly learned by foreign participants who are native speakers of non-tonal languages. We found that foreign participants could implicitly learn the phrase structure grammar on the carrier of Chinese tones, indicating that the phrase structure grammar could be generally implicitly learned as basic grammar rules of human language.What individuals implicitly acquire (i.e. rules or chunks) remains a long basic theoretical issue in the field of implicit learning. Experiment 1 indicated that the phrase structure grammar could be implicitly learned by native speakers of tonal languages as well as those of non-tonal languages. But it is still unknown whether the phrase structure grammar could be implicitly learned when the surface features of materials are obvious. Therefore, in experiment 2, we manipulated the strength of chunks and found that the phrase structure grammar still could be implicitly learned by both Chinese and foreign participants, In addition, all of them also learned the knowledge of chunks.Using functional magnetic resonance imaging (fMRI) technology, we explored the neural basis of implicit learning of the phrase structure grammar and the chunks knowledge in experiment 2. The phrase structure grammar was on the carrier of Chinese tones and the chunks were on the carrier of Chinese syllable. We found that the phrase structure grammar and the chunk knowledge could be both learned by participants. The activities in Broca’s region were associated with the processing of phrase structure grammar, while putamen and medial temporal lobe were related with the processing of chunk knowledge.On the basis of experiment 3, we further explored in experiment 4 whether the phrase structure grammar could be implicitly learned and its neural basis when this grammar and chunk knowledge were both on the carrier of Chinese tones. We found that the phrase structure grammar could be implicitly learned but chunks could not. The processing of phrase structure grammar was related with the caudate and Broca’s region.To sum up, results of the present study showed that:(1) the phrase structure grammar on the carrier of Chinese tones could be implicitly learned by foreign participants who are native speakers of non-tonal languages. Their performance on the task has no significant difference from that of Chinese participants, indicating that the phrase structure grammar could be generally implicitly learned as basic grammar rule of human language; (2) when chunks were added into the material, the phrase structure grammar still could be implicitly learned and even showed dominant effect; (3) the processing of phrase structure grammar is associated with Broca’s region, and the processing of chunks is associated with putamen and medial temporal lobe.