Neural Entrainment to Speech Analyzed with EEG a Review of Contemporary Theories About the Underlying Mechanisms of Speech Processing

Neural Entrainment to Speech Analyzed with EEG a Review of Contemporary Theories About the Underlying Mechanisms of Speech Processing

Linköping University | Department of Computer and Information Science Bachelor Thesis, 18 ECTS | Cognitive Science Spring term 2017 | LIU-IDA/KOGVET-G--17/019--SE Neural Entrainment to Speech Analyzed with EEG A Review of Contemporary Theories about the Underlying Mechanisms of Speech Processing Author: Richard Larsson Supervisor: Carine Signoret, senior lecturer, IBL at Linköping University Examinator: Fredrik Stjernberg, professor, IKK at Linköping University Copyright The publishers will keep this document online on the Internet – or its possible replacement – for a period of 25 years starting from the date of publication barring exceptional circumstances. The online availability of the document implies permanent permission for anyone to read, to download, or to print out single copies for his/hers own use and to use it unchanged for non-commercial research and educational purpose. Subsequent transfers of copyright cannot revoke this permission. All other uses of the document are conditional upon the consent of the copyright owner. The publisher has taken technical and administrative measures to assure authenticity, security and accessibility. According to intellectual property law the author has the right to be mentioned when his/her work is accessed as described above and to be protected against infringement. For additional information about the Linköping University Electronic Press and its procedures for publication and for assurance of document integrity, please refer to its www home page: http://www.ep.liu.se/. © Richard Larsson i Abstract Neural entrainment quite recently became considered an important mechanism used by the brain to process stimuli with periodic qualities, such as the frequency and duration time of signals reaching sensory organs. An increasing amount of data strongly implies that the brain might be using neural entrainment as a mechanism to either directly process speech and/or to facilitate speech interpretation. Neural entrainment is therefore a promising marker to use for research of speech perception. This literature review aims to summarize the most recent findings within this area with the end-goal to be used as a basis for designing an EEG experiment intended to analyze speech perception as a means to distinguish human voices. For this reason, data was collected from the scientific databases Europe PMC, Academic Search Premier, PsycINFO, PubMed, Scopus and Web of Science, where the keywords “EEG” + either the phrase “neural entrainment”, “neural oscillation”, or “cortical oscillation” were used to gather articles. Inclusion and exclusion criteria were then applied and the data was analyzed with the intention to answer the following research questions: “is it possible to observe neural entrainment to human voice/speech using EEG?”, “if so, what are the possibilities to use such neural entrainment as a marker for differentiating human voices from each other?” and “what is the nature of the mechanisms used by the brain to attain this entrainment?”. The resulting data from the articles indicated that, in order to yield reliable results when investigating neural entrainment to speech, the technique for analysis of brain activity could be done with EEG, a number of participants between 15-30 persons is enough, the spectral bands of interest are delta (<3 Hz), theta (4-8 Hz), beta (15-35 Hz) and gamma (>40 Hz), the method of analysis could be looking at both frequency and amplitude in the speech envelope, and finally the anatomical areas for investigating the brain’s ability to distinguish human voices using speech entrainment could be either areas within the auditory cortex or prefrontal areas involved in behavioral responses to speech processing. ii iii Acknowledgement I have attempted as best I could to complete tHis literature review, which is intended to elucidate the state of the concerned research field at present, to satisfactory standards. This work would have been a lot harder, not to say impossible, to accomplish without the continuous aid and patience with my many questions from the followinG people, whom I would like to thAnk for their kind assistance in this endeavor. My supervisor Carine Signoret, senior lecturer at IBL, for her invaluable guidance and support during this entire project, for her extensive proof reading of my drafts, and perhaps most of all, for giving me the idea for this thesis. My examinator Fredrik Stjernberg, professor at IKK, also him for his proof reading of my work, as well as for his most helpful comments and suggestions upon it. And last but not least, my esteemed classmates and group members of the thesis course, whom all kindly offered their much appreciated and helpful suggestions, namely the following persons: Sini Alhola, Ellinor Ihs Håkansson, Pontus Ohlsson, Elin Sjöström and Anna Tågmark, all third year students at the bachelor program in Cognitive Science, 2017. I thank you all for your invaluable assistance! Linköping, June 2017 Richard Larsson iv Contents Copyright .............................................................................................................................................. i Abstract ....................................................................................................................................................ii Acknowledgement ................................................................................................................................... iv 1. Introduction ..................................................................................................................................... 1 2. Theory and Background .................................................................................................................. 2 2.1 The Sound Signal and the Auditory Pathway ................................................................................ 2 2.2 Speech Perception ......................................................................................................................... 3 2.3 Neural Entrainment ....................................................................................................................... 3 2.4 The Importance of Neural Entrainment ........................................................................................ 4 2.5 Neural Oscillations ......................................................................................................................... 5 2.6 Current Theories of Speech Perception ........................................................................................ 5 2.7 Four Hypotheses for Neural Entrainment to Continuous Speech ................................................. 6 2.7.1 The Onset Tracking Hypothesis .............................................................................................. 6 2.7.2 Collective Feature Tracking Hypothesis ................................................................................. 6 2.7.3 Syllabic Parsing Hypothesis .................................................................................................... 6 2.7.4 Sensory Selection Hypothesis ................................................................................................. 7 2.7.5 Combining the Hypotheses .................................................................................................... 7 2.8 Prospects for Further Research ..................................................................................................... 7 3. Method ............................................................................................................................................ 9 3.1 Database Choice ............................................................................................................................ 9 3.2 Motivations for Keyword Choices and Final Keywords ................................................................. 9 3.3 Inclusion and Exclusion Criteria ................................................................................................... 10 3.3.1 Inclusion Criteria ................................................................................................................... 10 3.3.2 Exclusion Criteria .................................................................................................................. 10 3.4 Key Experimental Factors ............................................................................................................ 11 3.4.1 SJR and IF Scales ................................................................................................................... 12 3.4.2 Subsequent Factor Selection ................................................................................................ 12 3.4.3 Final Factor Analysis ............................................................................................................. 13 4. Results ........................................................................................................................................... 14 4.1 Article Selection Results .............................................................................................................. 14 4.2 Research Factors ......................................................................................................................... 15 4.2.1 Participants ........................................................................................................................... 15 4.2.2 Methodology .......................................................................................................................

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