Hello,

Can you help me to understand what exactly the "stimulusonset" in the data file is?

If I need only the "latency" of each answer, do I need to do anything with this column? I think that the "latency" of each stimulus is measured after "stimulusonset". So for getting the correct "latency" neither addition nor subtraction of "stimulusonset" is needed. Am I correct?

Another question:
The recorded "stimulusonset" in the data file is usually 0, 1, 2, 3... , however on Mac it is usually -15, sometimes -7 or -6. What does this mean? How can I get the correct "latencies" with negative "stimulusonsets"?

Thank you for your help,
Erzsebet

> So for getting the correct "latency" neither addition nor subtraction of "stimulusonset" is needed. Am I correct?

That is correct. By default latency is measured from the point the stimulus presentation sequence has finished. I.e. if you have

/ stimulustimes = [0=fixation; 2000=targetstimulus]

then latency is measured relative to the display of "targetstimulus", that is a latency of, say, 564 means the response occured 564 ms after the target stimulus. If you wish to measure latency relative to some other point, you can do so by specifying the <trial>'s /beginresponsetime attribute. E.g.

/ stimulustimes = [0=fixation; 2000=targetstimulus]
/ beginresponsetime = 0

would measure latency relative to the fixation stimulus.

Thank you, I understand that I do not have anything to do with little positive numbers.
But how can stimulusonset be negative?
The recorded "stimulusonset" in the data file is usually 0, 1, 2, 3... , however on Mac it is usually -15, sometimes -7 or -6. What does this mean? How can I get the correct "latencies" with negative "stimulusonsets"?
Thank you,
Erzsebet