Triggers timing Eprime

[Davide Baldo]

Hi all,

I designed an experiment where I am presenting videos and recording EEG (biosemi).

Some info:

• I am presenting videos (640x360, 30FPS, MP4) with E-prime, and each video lasts 30 seconds.
• I am sending a trigger at the beginning of the video via the serial port to Biosemi EEG (event task = onset time).
• And another trigger at the end of the video (finish time).

 

I was analyzing the triggers recorded in Biosemi, and I noticed that for a 30 seconds video if I compute the video stimulus by comparing when the first trigger was sent (video beginning) and when the second trigger was sent (video end) I get a length 29.5 seconds. 

There is an unusual half a second difference: Could it be that Eprime is presenting a 30 seconds video in 29.5 seconds (maybe skipping frames or something)?

I will double-check with a photo-diode but I was wondering if anybody had experienced something similar or if I'm doing something wrong with my triggers in Eprime.

Hope you can help,

 

Davide

[McFarlane, David]

Davide,

What mechanism do you use for outputting your triggers (Task Events,
Onset/OffsetSignal, inline code, etc.)?

What does your trial Procedure look like?

What PreRelease do you use on the object that presents the movie?

-- David McFarlane

On 2019-07-18 12:32 PM, Davide Baldo wrote:
> Hi all,
>
> I designed an experiment where I am presenting videos and recording EEG
> (biosemi).
> Some info:
>

> - I am presenting videos (640x360, 30FPS, MP4) with E-prime, and each
> video lasts 30 seconds.
> - I am sending a trigger at the beginning of the video via the serial

> port to Biosemi EEG (event task = onset time).

> - And another trigger at the end of the video (finish time).

[Mbarka Akounach]

Hello, 

for the first time I'm trying to send triggers from E-Prime to Biosemi. My paradigm is similar to yours;

Thank you 

Mbarka Akounach