Timing issue on every first stimulus in a loop with Psychtoolbox

Hi,

I am currently facing timing issue with Psychtoolbox. Indeed, in my script there is a loop displaying the same stimulus several consecutive times. Each trial this loop is called and each trial the first stimuli is displayed for a shorter duration or longer duration (about one frame) than the expected duration. Then the timing is perfect the rest of stimuli. I guess it is a synchronization issue because it is exactly the same loop, which display the stimuli every time. Has anyone ever had this problem?

Best,

Simon

[Walter Roberson]

Synchronization of stimuli is handled by Psychtools extensions to MATLAB using code that is not part of MATLAB . The matter should be taken up with PTB.