TTL insertaion

[mickeyi]

Unfortunately that won't work. We use TTLs for an EEG system and my EEG hardware only recognizes the start of a TTL... Is there any way to "hardcode" a TTL into a movie? Any other way around this? I imagine this could be useful for people who do work with psychophysiology and want to "time-lock" the response to a specific event in a movie.

[jarvis24]

Actually, it just occurred to me that you could do this the way you want. Show the movie with a time value of 0ms. THEN insert a blank stimulus "~" with a LOC value of "0,0,0" with a time value that corresponds to when you want the TTL signal to occur. THEN send the TTL signal. I think that ought to do it.

[mickeyi]

OK. Let me see if I understand the logic. Let's say I want to show a 15 second movie, and I want a TTL sent at 9.8 seconds. To do this I would show the movie with a time of 0, and then send an empty stim with a time value of 9800 (the movie will still show because we didn't clear the previous screen, right?), ans then send a TTL at port 888 for say 5ms. Is this right? Also, will the movie play till the end of the 15 ms?

Thanks!

[jarvis24]

Yes, I expect that is how it would play out.

[obhi_lab]

Hi. I discovered this thread while working on the same problem: trying to send a TTL during the display of a movie (.avi) stimulus----e.g., the movie we wish to display is about 6 seconds long and we wish to deliver a TTL to an external device during this 6-second clip. I've tried the suggested work-around but (a) the movie gets cut short or doesn't play at all and (b) the TTL is not successful... advice? thx in advance!
cheers

[jarvis24]

Thanks for the info--would you mind posting your input file so I can try running it here? Please zip and attach any necessary files to replicate the problem.

[mickeyi]

I have finally come around to trying this, and it didn't work for me either. It seems like the empty stim (~) is replacing the video so that the video only shows for a short period of time (a few milliseconds). I haven't yet tested whether the TTL will send (I'm not at my EEG machine right now). Obviously this won't for me. I've attached the file and I used as an example. I'd appreciate your help with this as soon as you can--I thought this work-around was going to work and we're setting to start running our study soon. Yikes!