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Controlling exposure duration, inter-trial and inter-stimulus intervals

mongrel — Mon, 05 Dec 2016 08:01:36 GMT

Hi Dave,

I have a question concerning control of timing. I have read this: http://www.millisecond.com/support/docs/v5/html/howto/howtocontroltiming.htm. However, I still have questions.

I have only two trials (containing two stimuli) that I would like to be randomly displayed in one block (12 times, replace and repeat). I do not want the participants to respond to anything. One trial should look like this:

Stimulus 1 (1500ms), ISI (100ms), Stimulus 2 (1500ms). Between two trials, I would like to have an ITI of 1500ms.

The second trial should look accordingly but with different stimuli.

Are the pre- and the posttrialpause attributes, what actually gives me the ITI, so do I have to split it on the two? I know, the ISI is controlled by the stimulustimes, but it never seems to works properly. I think, I probably could work with the parameters, but I do not really understand, how.
Further, the block only seems to work, if I use noreplace, which I don't want...

<trial OWpos>
/ stimulustimes = [1000= picture.FocalOW; 1100= picture.USpos]
/ validresponse = (noresponse)
/ posttrialpause = 500
/ trialduration = 4600
</trial>

<trial YMneg>
/ stimulusframes = [1000 = picture.FocalYM; 1100 = picture.USneg]
/ validresponse = (noresponse)
/ posttrialpause = 500
/ trialduration = 4600
</trial>

<block all>
/ trials = [1-12= noreplace(OWpos, YMneg)]
</block>

Thank you very much in advance,

M.

RE: Controlling exposure duration, inter-trial and inter-stimulus intervals

Dave — Mon, 05 Dec 2016 08:01:36 GMT

[quote]

[b]mongrel - Monday, December 05, 2016[/b]

Hi Dave,

thanks for the reply! What actually does set the exposure duration of the second stimulus? The trial-duration?
And if so, I would choose a 3100-duration to ensure that stim1, stim2, and ISI are covered by that duration (1500ms+100ms+1500ms=3100ms), correct? Unfortunately, that is not working,the second stimulus is only presented very shortly.

Here is an example:

<trial DUSneg5>
/ stimulustimes = [0 = picture.D5; 1500 = ISI; 1600 = picture.DUSneg5]
/ validresponse = (0)
/ posttrialpause = 1500
/ trialduration = 3100
</trial>

What am I still doing wrong?

Thanks again!
M.

[/quote]

> What actually does set the exposure duration of the second stimulus?

The stimuli are erased when the trial ends / enters its /posttrialpause. /trialduration *includes* /posttrialpause. See the "How to Control Trial Duration and Inter-Trial Intervals" topic in the documentation re. how the various timing components involved in a <trial> relate to each other.

RE: Controlling exposure duration, inter-trial and inter-stimulus intervals

mongrel — Mon, 05 Dec 2016 03:29:28 GMT

Hi again,

for, now, I solved it like this:

<trial DUSneg6>
/ stimulustimes = [1 = picture.D6; 1500 = ISI; 1600 = picture.DUSneg6; 3100 = ISI2]
/ validresponse = (0)
/ posttrialpause = 1500
/ trialduration = 4600
</trial>

Is there a better way?

RE: Controlling exposure duration, inter-trial and inter-stimulus intervals

mongrel — Mon, 05 Dec 2016 03:10:18 GMT

RE: Controlling exposure duration, inter-trial and inter-stimulus intervals

Dave — Thu, 01 Dec 2016 10:31:14 GMT

[quote]

[b]mongrel - Thursday, December 01, 2016[/b]

[/quote]

What gives you an "ISI" is displaying a "blank" stimulus at the desired time in /stimulustimes. To implement

> Stimulus 1 (1500ms), ISI (100ms), Stimulus 2 (1500ms).
> Between two trials, I would like to have an ITI of 1500ms.

you do

<trial example>
/ stimulustimes = [0=stimulus1; 1500=ISI; 1600=stimulus2]
/ posttrialpause = 1500
/ trialduration = 4600
/ validresponse = (0)
</trial>

<text stimulus1>
/ items = ("This is stimulus 1")
</text>

<text stimulus2>
/ items = ("This is stimulus 2")
</text>

<shape ISI>
/ shape = rectangle
/ color = white
/ size = (100%, 100%)
</shape>