Millisecond Forums

I'm recording Inquisit data simultaneously with eeg via either Cedrus stimtracker or just homemade VCP device, and latencies in eeg marks are consistently larger, than in Inquisit data files - 200 ms for pictures, 345 ms for following keyboard response. It seems like this lag is growing during the trial and depends on scenario structure, but I cannot check it yet, and it doesn't vary between multiple runs and participants.

This alone isn't really a problem, since lags are constant between cases and I can recalibrate all my analyses, it's weird stuff about consistency: in inquisit data pictures show latency exactly as programmed in scenario and larger in eeg, but response times are reasonable in eeg and often outright impossibly tiny in inquisit data - to get 80ms response time in Stroop test you have to start motion before you see picture, but most participants score 100% of correct responses.
And no, don't try to say that it may be actual time - I triple-checked all publications I could find on this paradigm and sure that response time cannot drop significantly below 300ms without lowering correctness of response.
When I record inquisit session without eeg, response timing is the same, statistical checks show no significant differences and impossible times are still there.

Question is: where is this time actually lost and how can I know true response latency? Especially in case i don't have any sort of simultaneous record to evaluate this lag (and every simultaneous record will contain its own lags anyway).