![]() Note: Our subject screen was connected via Display Port on the Nvidia graphics card. Let us know if there is anything else we can try to get the display lag down from two frames to one. Please find the photodiode signal analysis plots attached (both in photodiode tuner and timing script v1). This is great news for us! Though we are puzzled why a very early or a very late screen flip command give consistent delays but scanline threshold values in between do not. As a result we are also getting the stimulus presented on screen for the expected durations (here 200ms / 12 frames). We ran the timing script v1 task as before using scanline threshold set at 0 in photodiode tuner for a total of 520 stimulus presentations and we observed a constant delay in stimulus flipping to the screen. With the threshold set to 0 or 760 we are able to get a consistent screen flip after a delay of two frames! (we just tried these two extremes in the tuner application along with many values in between).ģ. With photodiode scanline threshold at the default value of 690 (for a monitor height of 768 px), the issue of inconsistent delays in flipping the stimulus to the screen remained. We had a go at measuring the stimulus durations with the new MonkeyLogic packages that you mailed and we have some interesting analysis results:ġ. Pardon me for getting back late over this weekend. Please let me know if any further information is required. We would really appreciate any and all help in rectifying this issue at the earliest. ![]() I can further share the exact codes we ran to present the stimulus if needed. I have attached a figure summarizing our analysis of this with the following presentation methods: We are a bit baffled by this as the above observation suggests that it is possible to present stimuli very consistently using the same system and monitor. We observed consistent delay and expected stimulus display duration as per instruction in the code. To understand if the issue was a monitor/driver related issue, we coded up a very similar task in Psychtoolbox and measured the delay in change of photodiode signal from the eventmarker and also the stimulus display duration. This is major issue for us as we are interested in recording neurophysiological data from behaving macaques. We observed that the latency between the eventmarker sent in toggleobject() and deflection in photodiode signal was not a constant value (was bimodally distributed in general) which furthermore lead to variation in stimuli display duration. Using toggleobject(), we are flipping on the stimuli and concurrently sending digital eventmarker (with strobe) to the external DAQ. To measure actual screen flip times, we have attached a photodiode onto the subject screen whose signal we are sampling at 25kSps in an external DAQ (eCube server). ![]() We have setup a fixation task (8 stimuli per trial, 200ms stimulus presentation and 200 ms ISI, stimulus is a white screen and ISI is black screen) using the timing script v1 method in MonkeyLogic. Subject screen: Elo 1593L RevB PCAP touchscreen, 1366px by 768px, 60 Hz framerate.Ĭontrol screen: Dell P2419H, 1920px by 1080px, 60 Hz framerate. We are currently facing an issue with the consistency of stimulus flip-times which further affects the stimulus durations on screen also.
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