Hi there,

I have a question about how inquisit deals with stimuli that are presented and then replaced within the timeframe of a single vertical refresh - I've had a quick look through the forums to see if anybody else has asked this but I can't find anything (though though that may just be my inept searching!).

I have a trial sequence that is set to display stimuli using the stimulustimes command (rather than specifying the number of frames a stimulus should be on for), and there are stimuli due to be presented at short enough intervals that more than one stimulus change is supposed to happen within a single vertical refresh rate - that is, in the space of <16.7 ms (the duration of a single refresh on a 60Hz monitor), my trial sequence orders a stimulus to be rendered (which I realise would usually happen on the next refresh, whenever that may be) AND replaced by a second stimulus in that time frame. My question is, if this happens, does the original stimulus never get show, or do they both get presented together at the next refresh? If so, would they appear on top of oneanother for this frame?

Take the following sequence for example - stimulustimes = [0=cross; 700=forwardmask; 950=shapeerase; 960=practisecentre; 1460=shapeerase; 1470=backwardmask] - as the shapeerase is only presented for 10ms, and this is less than the refresh rate of most monitors, will it just get presented at the same time as the subsequent stimuli, and never on its own? Or will it be missed out completely?

Thanks in advance for any answers, apologies if it's a really obvious question!

Sarah

Inquisit will pick the closest possible value (i.e. frame) to the times you entered, i.e. stimuli might be shown a little earlier or later than the specified time. Stimuli falling within the same frame by that logic will effectively be presented at the same time. I suggest you generate some test data and inspect the stimulusonset columns closely.

Hope this helps,

~Dave

Thanks Dave - I assumed this is probably what it would do, and just pick the closest frame. However, when I run test data, the stimulus onset columns all tend to say zero, which is somewhat confusing. Any ideas (without me posting my whole code) if there's something obvious I might be doing wrong that might be causing this not to record?

I am therefore struggling to work out whether the very short stimuli gets presented at all - especially as they are all centred around the same spot, so I suspect if it is trying to display two at the same time then one will be overwritten by the other anyway?

Thanks

Sarah

Not sure about the prevalence of 0s in your stimulusonset columns. Normally, you should have one such column for every stimulus element displayed in a given trial with the value reflecting the time in ms when Inquisit initiated the display of the respective stimulus (measured from the onset of the trial). You might want to check if your version of Inquisit is up-to-date and do the same for your graphics system (driver, DirectX, etc.). BTW, related timing questions have been discussed at greater length in these threads (beware partly technical reading):

• http://www.millisecond.com/forums/Topic3649.aspx#3649


• http://www.millisecond.com/community/forums/p/1224/3664.aspx#3664


• http://www.millisecond.com/community/forums/p/1443/4797.aspx#4797

If the stimuli indeed end up being displayed in the same frame (do the math), then the ones on the "bottom" (i.e. listed first) will effectively not be displayed.

~Dave