1. Royal Visio, National Foundation for the Visually Impaired and Blind, Oud Bussummerweg 76, 1272 RX Huizen, the Netherlands
2. Behavioural Science Institute, School of Educational Science, Radboud University Nijmegen, Postbus 9104, 6500 HE, Nijmegen, the Netherlands
3. Royal Visio, National Foundation for the Visually Impaired and Blind, the Netherlands
4. Royal Kentalis and Behavioural Science Institute, School of Educational Science, Radboud University Nijmegen, the Netherlands
5. Behavioural Science Institute, School of Educational Science, Radboud University Nijmegen, the Netherlands