1. Speech Signal Processing Laboratory, Department of Computer Science, University of Crete, Heraklion Crete, Greece
2. Department of Theoretical and Applied Linguistics, School of English, Aristotle University of Thessaloniki, Thessaloniki, Greece
3. Department of Educational and Social Policy, University of Macedonia, Thessaloniki, Greece
4. School of Informatics, Aristotle University of Thessaloniki, Thessaloniki, Greece