1. Stichting OOK-OC, Research Center for Augmentative and Alternative Communication, 5482 JH Schijndel, The Netherlands
2. Stichting Milo, Intervention Center for Augmentative and Alternative Communication, 5482 JH Schijndel, The Netherlands
3. Department of Pedagogical Sciences, Radboud University, 6525 XZ Nijmegen, The Netherlands
4. Behavioral Science Institute (BSI), Radboud University, 6525 XZ Nijmegen, The Netherlands