Using CRT monitor and stimtracker

Hi, I am using a CRT monitor to work with StimTracker. When the target starts, the white square (with a black background) also appears so the light sensor detects the light. But the light sensor sends the onset signal to Biosemi during the presentation of the white square continuously. I guess this is because the CRT is building the screen. But is there any possibility to fix that so light sensor only sends signal to Biosemi once (just like using a LCD monitor)?
Thank you. Look forward to your reply.

Unfortunately not. This is an issue that didn’t come to our attention until another CRT user mentioned it. We will keep it in mind for a next revision of StimTracker.