Log Files - More Data!
Log Data Files contain all of the columns contained in the Short Data File as well as these additional columns:
Date the session was run
Time the session was begun
Name of the input file
Number of milliseconds expired between the start of the first trial and the beginning of the current trial. Keep in mind that the trials are written to the data file in their origional order-not the order in which they were presented. If you want to follow the time sequence, you can sort the data file by the Order column. This value is the actual difference in the two times and is independent of all other time measures.
The number of milliseconds it took DirectRT to prepare all of the screens for the current trial. This is done during the interval for the trial and does not add to the time it takes for the trial to execute. This is important to monitor though. You want to make sure that this value never exceeds the actual trial interval value that you've specified. This is usually not a problem, but you can verify this by examining the TotalInt value (next column).
This is the amount of time from the end of last stimulus screen of the previous trial to the beginning of the first stimulus screen of the current trial. This value should approximate the value in the Style file, Options->Trial Interval. Very slight variations in this value between trials is normal (about 10ms). Timing then becomes precise at the start of the first stimulus. If you find a TotalInt value that significantly exceeds the trial interval you specified, this can mean you have not set a sufficiently long interval such that DirectRT can prepare all of the stimulus screens before your interval is up. In such cases, try extending your trial interval.
The name of each stimulus screen subsequent to the trial interval
The actual display time for each stimulus screen. You might notice that the display time for the final stimulus is usually a little bit longer than the RT value (e.g., 1-15ms longer). This is because the time at which the subject responds is not the exact time at which the stimulus leaves the screen. Depending on how early into the screen refresh cycle the response occurs, the stimulus may be displayed for an additional number of milliseconds.
Doing the math if you're interested
If you want to account for where all the time has gone, then sort your data by the Order column (or the Started@ column) so that the trials are in their temporal order. If you take the trial's start time (Started@) and add the trial interval (TotalInt) and each of the Time n values, then this should add up to the Started@ value of the subsequent trial.
Do not include the LoadTime value because this is going DURING the trial interval.
Make sure you don't have any missing trial data if you're going to do this (e.g., this won't work if you have omitted trial data from the data file by specifying a Block ID of 0-at least for trials surrounding this missing trial(s)).