No response to key press in certain trials

[Tolliverr]

Hello,

I am using DirectRT to create a sustained attention to response (SART) task. In the task, subjects must press the space bar when any number except 3 appears on the screen. When 3 appears, a "no response" is considered correct. Each stimulus stays on the screen for 250 ms. I have a 1125ms delay in between each stimulus.

The problem is that sometimes the program does not advance on to the next stimulus in the sequence, even when a response is entered. However, at these times if you press the space bar a second time the program will advance. It seems like the initial space bar press doens't register at times. This will happen at different trials each time the program is run, and I can't figure out the reason.

I have attached my input file.

[Tolliverr]

I have been experimenting with the program more, and it seems that the issue is when subjects respond to the number stimulus quicker than around 200 ms. Is this something that can be fixed?

Thank you.