EPrime - motion stim issues

[Lisa Levinson]

 I am looking to replicate an experiment originally created in Presentation
for use with EPrime, part of an EEG experiment. The original experiment used
that software’s programming language to create a color and motion stimulus
that allowed the researchers to compare the parvocellular and magnocellular
visual pathways. I do not know EBasic and so I have created the color stim
in Photoshop and imported the image as a slide. While I am not able to
control luminance it appears very close to the original. The motion stim is
proving much more complicated. I created a vertically oriented sinusoidal
spatial frequency grating as an animation file in Final Cut (editing
software) and have been struggling ever since to make it work as intended.

The experiment calls for a low frequency grating to traverse from left to
right for 100ms with inter-stimulus intervals anywhere from 500 ms to
1000ms. Because the stimulus presentation is so short I don’t seem to be
able to use the video start/stop feature; additionally, randomizing the ISI
is not possible using this feature. I determined that one cycle of the
animation sequence is 31 frames and with a 60 frame per second animation
that means that I have 10 six frame sets per second (each set 100ms). I then
created 6 frame .avi files and loaded them sequentially. Because the
experiment calls for 320 trials I had the choice to load 320 files or create
a loop with 5 six frame sets, I opted for the loop. To allow for the
randomized ISI intervals I created jpeg files containing the final frame of
each set and then finished the sequence with my one remaining frame (5 six
frame sets plus one final still, making 31 frames).

After loading the movie/still files (sequentially) it seems that even though
the stills(jpegs) were captured from the animation frames they are not
similar in size, so I have an inconsistency there – issue one. The other
issue is that the two images (movie/still) overlap rather than following in
sequence. One appears inside the other and the error message I get once I
abort is “unable to update frame.” I did eliminate the 500ms ISI but that
has not helped. I also tried to eliminated the jpeg files but then I can
only randomize the duration of the motion which should be consistent at
100ms intervals. It is the time between presentations that should randomly
fall within 500 to 100ms.

I am at a complete loss as to what to try next. HELP!

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