Dear Andrew, On 18.01.2010, at 20:08, Andrew Straw wrote: > Jens Kremkow wrote: >> Dear all, >> >> I am using noise stimuli in which the exact content of each frame is >> important for the analysis at a later stage. >> My, I hope simple, question is: what happens on the screen when a frame >> is dropped? >> >> Does it work like this: >> >> frame[0] ok -> frame[0] on screen >> frame[1] dropped -> frame[0] on screen >> frame[2] ok -> frame[2] on screen >> >> Or is it more complex? > > Hi Jens -- it depends on how you're generating the frames. If you're > doing a simple playback like: > > for i in range(10): > draw_image(i) > screen.swap_buffers() > > then you will get the following space-time diagram for an X moving to > the right at constant speed (view with monospaced font): > > space ----> > > t __X______ > i ___X_____ > m ____X____ > e ____X____ > | _____X___ > | ______X__ > | _______X_ > v ________X > > > In other words, the draw_image() function doesn't know a frame was > skipped, and so the diagonal line in space-time gets a constant time offset. > > On the other hand code like: > > for i in range(10): > draw_image_for_time( get_current_time() ) > screen.swap_buffers() > > Will do this: > > space ----> > > t __X______ > i ___X_____ > m ____X____ > e ____X____ > | ______X__ > | _______X_ > | ________X > v _________ > > In this case, the overall diagonal line in space-time is maintained, but > there is a momentary glitch at the frame skip. Most of the VE stimuli, > e.g. the sinusoidal gratings, are of the second type. > > I hope that helps. > It indeed helped my understanding. Thanks a lot for responding so quickly. Regards, Jens > -Andrew > -- > Andrew D. Straw, Ph.D. > California Institute of Technology > http://www.its.caltech.edu/~astraw/ > ====================================== > The Vision Egg mailing list > Archives: //www.freelists.org/archives/visionegg > Website: http://www.visionegg.org/mailinglist.html =====================================The Vision Egg mailing list Archives: //www.freelists.org/archives/visionegg Website: http://www.visionegg.org/mailinglist.html