Psychtoolbox flip time issue

Question

I am running a psychophysics task on psychtoolbox that need to show each image for 16, 30, 60, and 120 milliseconds. Although my system monitor refresh rate is 16.66 ms (60 Hz) but the lowest time I get is almost 33 ms (I check this time by recording video from the screen while showing these images).

I've searched a lot and now I use flip with specifying the time with ifi and nextFrameInterval but still can't show my image for 16 milliseconds. Why is this happening and how can I fix this?

ifi = Screen('GetFlipInterval',window);

Screen('DrawTexture',window,fixation,[],fixRect);
[~,lastVisualInterval] = Screen('Flip', window);

nextStimFrameDelta= (p.pre_mask_time/ifi);
Screen('DrawTexture',window,stimulus(rec(TrialNum, 3)),[],rectStim);
[~,lastVisualInterval] = Screen('Flip', window,lastVisualInterval +((nextStimFrameDelta-0.5)*ifi));

nextStimFrameDelta= ((rec(TrialNum,2)/1000)/ifi)  % rec(TrialNum,2) is the duration of peresenting images (16,30,... ms)
Screen('DrawTexture',window,mask(TrialNum),[],rectStim);
[~,lastVisualInterval] = Screen('Flip', window,lastVisualInterval +((nextStimFrameDelta-0.5)*ifi));
% And here the facial expression must be replaced by a mask after 16 or 30,... ms

Please edit your question to include an example of your current code for stimulus presentation. — DMR, Dec 10 '22 at 16:44
Please provide enough code so others can better understand or reproduce the problem. — Community, Dec 11 '22 at 19:45
What is the value of the variable 'dec' that you have in the last Screen Flip? — DMR, Dec 13 '22 at 05:26
It is 0.5, I have edited the previous Flip line, but I've forgotten to change this one. — Helia Taghavi, Dec 14 '22 at 14:45

Psychtoolbox flip time issue

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