[open] Start Response Interval-checkbox missing in sketchpad

Cageman

Hello,

I'm starting to use OpenSesame 0.27.3.
While implementing a visual stimuli with a sketchpad I noticed that the 'Start response Interval'-checkbox is not there anymore? Is there a special reason for this?

I would like to measure a persons responsetime from the start of a stimulus.
Now I (manually) have to correct the response-time afterwards.
This is getting very complex because the stimulus-time can be variable.

Is there an other way to measure responsetime from the start of a stimulus?

Regards,
Peter

sebastiaan

Hi Peter,

The 'Start response interval' option has been removed, because it turned out to be confusing to many users. (People assumed that enabling this option would start the actual response collection.) The functionality is still accessible through the script of the sketchpad item though. The following line will mark the onset of the sketchpad as the start of the response interval:

set start_response_interval "yes"

Alternatively, you can set the start of the response interval in a Python inline script, like so:

# Set the start of the response interval to the current time
exp.set('start_response_interval', self.time())

Cheers!
Sebastiaan

Cageman

Hi Sebastiaan,

Thanks for your quick reply!
Ok, the checkbox is removed because of confusion.
But on the other hand you now can get the situation that unexperienced people (our first year students) need to make changes in a (sketchpad)script.

One question comes to my mind about the exact start of the response interval:
Is the start of the response interval synchronized with the appearance of the visual stimuli (or is it synced with the vertical refresh of the display)? If not, how can this be achieved?

If the display has a refresh rate of 50Hz it takes 20ms to refresh the screen.
This means that after the start of the response interval there can be an uncertainty up to 20ms.

Thanks in advance!
Regards,
Peter

sebastiaan

One question comes to my mind about the exact start of the response interval: Is the start of the response interval synchronized with the appearance of the visual stimuli (or is it synced with the vertical refresh of the display)? If not, how can this be achieved?

Whether the display timestamp corresponds to the moment that the monitor starts a new refresh cycle (i.e. blocking) or the the moment that the display is sent to the graphics card (i.e. non-blocking) depends on the back-end. The legacy back-end is non-blocking, whereas the xpyriment and psycho back-ends generally speaking use blocking presentation. You can read more about this here:

• http://osdoc.cogsci.nl/miscellaneous/timing/

For the purpose of running time-crucial experiments, blocking presentation is preferable, as you point out. But not all systems support this.

Cheers!