Dear Andrew, thank you so much for your help and suggestions...now triggers work great and have a perfect timing! I have a new question...I have a grey background and I need to draw two squares that flicker at various temporal frequencies (for example one square flickers at 8 Hz and the other one flickers at 12 hz). Do you know if I can do that with Vision Egg and how? Thank you so much! Alessandra =====================================The Vision Egg mailing list Archives: //www.freelists.org/archives/visionegg Website: http://www.visionegg.org/mailinglist.html