I have a problem with my output. My experiment is set up so that three events (a fixation, another text file and a sound file) all present concurrently, this makes each trial one stimulus item. I use blocks to displays a 28 of these trials in which are 4 target trials/items that require a mouse press response.
When I run it through without responses the cumulative time increases by 264ms for each trial and does so like clockwork.
I thought I would be able to get reaction times using the cumulative time and reaction time columns: minus the cumulative time for the presentation of the target trial from the cumulative time of the trial in which the response is made and add the reaction time.
However, I have noticed that this seems low, but the cumulative time from the trial in which the response is made and the trial following it is oddly high - no longer the regular 264.
Each visual event of each trial is the last to present and is set to end only after 200ms, and as mentioned above, when run without responses being made the trials present every 264ms. I have also noticed that according to the cumulative time output some of my target trials are being presented for less than 200 ms. This is no doubt why the reaction times seem low.Is this a problem with the presentation timing? or of the output cumulative time recording?
It’s difficult to tell exactly what’s going on without seeing the experiment itself. However, I can infer that you have your 200ms events set to end on a response OR a time limit. This makes sense, since the only trials that are shorter than 264ms are the ones with a response. For the most part, the trials longer than 264ms are the trials immediately after a response, which seems to me to imply that you’re waiting for the key release before moving on.
If I had to make a wild guess about your refresh rate, I’d suspect your monitor is set to 120Hz, since these numbers appear to be rough multiples of 8ms.
All of this is just speculation. I can’t do better than this without seeing the experiment itself.