Hi everybody,
setup:
Mac OS 9.2,
MATLAB 5.2.1.1421,
PsychToolbox 2.52,
Eyelink II,
Eyelink Toolbox
monitor refresh rate 120 Hz
screen resolution: 1024x 768 pixel
I am working on saccade contingent experiments having people read
single sentences.
I have three types of delay: the eye tracker delay (at least 3 ms),
the drawing delay, and the display delay.
this is a short description of the code:
screen(visual.main,`WaitBlanking');
time_on = getSecs * 10000;
- online saccade detection (reading out the link)
- computations
t2 = getSecs * 10000 time_on;
CopyWindow (I copy a 1024 x 20 pixel rect [0 374 1024 394] from an
OFF screen to the main screen) using scrCopyQuickly
t3 = getSecs * 10000 time_on;
As I read in another message, `CopyWindow' runs synchronously meaning
that a call to Screen(`CopyWindow') does not return until it has
finished copying.
t3 t2 is on average 0.68 ms
I thought that t3 is the time the new rect is appearing on the screen.
Obviously, this is not the case.
Can anybody tell me how long it takes between t3 and the actual
appearance on the screen (t4). How can I measure it? On what does it
depend? Does it take more than 1 ms (roughly)?
The underlying logic is the following:
On the vertical axis, the to be copied rect is in the middle of the
screen. With a refresh rate of 120 Hz (=8.3 ms for a refresh), the
pointer (or whatever it is) is getting to the critical area after
around 4 ms.
Therefore, t3 (or t4?) has to be smaller than 4 ms.
Until now, I relied on t3 (time at which CopyWindow returned) with
the following logic: If t3 (recomputed as an absolute measure) is
smaller than the time of saccade end (which I can reliably
determine), then I conclude that the subject didn't see the display
change since we're supposed to be visually blind during a saccade. I
don't want the subject to see the display change.
I tested myself and according to my analyses I wasn't supposed to see
any of the display changes, but on quite a few occasions I definitely
did. Therefore, I think I have to know how long it takes between the
return of CopyWindow and the actual stimulus appearance on the screen.
Any help is highly appreciated.
thanks a lot
Antje Nuthmann
setup:
Mac OS 9.2,
MATLAB 5.2.1.1421,
PsychToolbox 2.52,
Eyelink II,
Eyelink Toolbox
monitor refresh rate 120 Hz
screen resolution: 1024x 768 pixel
I am working on saccade contingent experiments having people read
single sentences.
I have three types of delay: the eye tracker delay (at least 3 ms),
the drawing delay, and the display delay.
this is a short description of the code:
screen(visual.main,`WaitBlanking');
time_on = getSecs * 10000;
- online saccade detection (reading out the link)
- computations
t2 = getSecs * 10000 time_on;
CopyWindow (I copy a 1024 x 20 pixel rect [0 374 1024 394] from an
OFF screen to the main screen) using scrCopyQuickly
t3 = getSecs * 10000 time_on;
As I read in another message, `CopyWindow' runs synchronously meaning
that a call to Screen(`CopyWindow') does not return until it has
finished copying.
t3 t2 is on average 0.68 ms
I thought that t3 is the time the new rect is appearing on the screen.
Obviously, this is not the case.
Can anybody tell me how long it takes between t3 and the actual
appearance on the screen (t4). How can I measure it? On what does it
depend? Does it take more than 1 ms (roughly)?
The underlying logic is the following:
On the vertical axis, the to be copied rect is in the middle of the
screen. With a refresh rate of 120 Hz (=8.3 ms for a refresh), the
pointer (or whatever it is) is getting to the critical area after
around 4 ms.
Therefore, t3 (or t4?) has to be smaller than 4 ms.
Until now, I relied on t3 (time at which CopyWindow returned) with
the following logic: If t3 (recomputed as an absolute measure) is
smaller than the time of saccade end (which I can reliably
determine), then I conclude that the subject didn't see the display
change since we're supposed to be visually blind during a saccade. I
don't want the subject to see the display change.
I tested myself and according to my analyses I wasn't supposed to see
any of the display changes, but on quite a few occasions I definitely
did. Therefore, I think I have to know how long it takes between the
return of CopyWindow and the actual stimulus appearance on the screen.
Any help is highly appreciated.
thanks a lot
Antje Nuthmann