First of all, I would like to thank my supervisor, Dr. Márk Jelasity, for guiding and supporting my research and providing the opportunity to work on fascinating topics.Next, I would like to thank my colleagues who helped me to discover interesting areas of science and helped give birth to new ideas during our discussions. In alphabetical order, they are Dr. Árpád Berta, Dr. István Hegedűs and Dr. Róbert Ormándi. I would also like to thank David P. Curley for correcting this thesis from a linguistic point of view.Last but not least, I would like to thank my family and friends for supporting me all this time.