2 Literature Review
2.1 Linguistic Features in Coh-Metrix
The development of various fields like computational linguistics, discourse processing,corpus linguistics, information extraction, and information retrieval has made it possible toinvestigate computational measurements of linguistic features. Coh-Metrix is a web-basedtext analysis tool that integrates various technologies in computational linguistics and corpuslinguistics. It can automatically analyze 106 lexical grammatical and semantic features of onetext[2]. The features that Coh-Metrix extracts cover 11 dimensions: Descriptive, ReferentialCohesion, Latent Semantic Analysis, Lexical Diversity, Text Easability Principal ComponentScores, Connectives, Situation Model, Syntactic Complexity, Word Information, Readability,and Syntactic Pattern Density[3].
2.1.1 The Descriptive Indices and Word Information
Coh-Metrix 3.0 provides descriptive indices to help the user check the Coh-Metrixoutput and interpret data patterns. In the descriptive indices group, 11 indices are calculated tomake sure that numbers make sense. These indices, including number of words, number ofparagraphs, and number of sentences, count the number of paragraphs, sentences, and wordsin a text. The number of sentences in a paragraph (mean, standard deviation), the number ofsyllables (mean, standard deviation), and the number of syllables (mean, standard deviation)in a text can represent the paragraph length, the sentence length, and the word length.Calculating these descriptive indices can indicate if the speakers will use sufficient and properwords to express their ideas. As for proficiency speakers, they will use adequate andappropriate words to deliver information in a speech. Besides, according to Zipf’s[4] law,infrequently used words in a language tend to be longer, so the word length may be a proxyfor prior knowledge about the topic. From this perspective, these indices can illustrate thespeaker’s language level.
2.2 Public Speech and its Linguistic Features
2.2.1 Definition of Public Speech
Developments of public speaking have a long history in the West. The research on publicspeech originated in the Greek city-states around the 5th century BC. These countries oftenuse public speaking and debating to decide public affairs. Therefore, the practice of publicspeech has been extensively developed. The materials of this paper are explanatory text whichis consistent with the TED (Technology, Entertainment, and Design) style. “TED is designedas a nonpartisan nonprofit devoted to spreading ideas, usually in the form of short, powerfultalks.” TED speeches cover all subjects, which is an important resource for English learners.
According to Lucas[1], public speaking is the process or act of performing a speech to alive audience, which is commonly understood as formal, face-to-face speaking by a singleperson to a group of listeners. Public speech has played a significant role in education,government, and business, such as classroom presentations, inaugural addresses, andconference speeches. In fact, it is believed that people in almost every industry now are askedto possess communication skills, including public speaking. Therefore, public speech hasbeen considered an efficient and popular way for people to convey their opinions and expresstheir feelings.
According to Wang[22], when speakers talk with di
