maintaining serial-choice RT dual-task timing

Marton

(reposting this here as there been no response in the original thread - for context see http://forum.cogsci.nl/index.php?p=/discussion/3558/dual-task-timing)

Hello again Roelef,

I have finally gotten around to implementing your fix - I have recoded the dual task via a single canvas item that is then run and generates the appropriate stimuli via the position and colour variables. While this method has tightened up the presentation timings, I am still unable to maintaining a stimulus presentation rate that is within less than 100ms of the intended presentation rate.

One added bit of compication is that in order to maintain a consitent presentation rate regardless of response times, I have had to add a pause between stimuli which has a presentation duration calculated on the basis of the difference between the last RT and intended presentation interval - so if intended presentation interval is 1000ms and a participant responds in 500 ms, a 500 ms 'pause' (an blank frame) is presented before the next stimuli.

Attached below is example code + file pool images its using to maintain a 1000ms presentation rate (note - I am using the sound recorder plugin to capture audio responses during the dual task. I have left this functionality in for testing purposes)

with this code, the best timing performance I can get (using psychoPy@640x480) is a true presentation rate of average ~1130ms.

I have also tried stripping out the pause related components and just have essentially all stimuli timing out due to no response, resulting in an average true presentation rate of ~1100ms.

Is there any way to get this presentation rate closer to the intended presentation rate for the task or is this stimulus presentation time unavoidable? If this prep time is unavoidable then I can end up using a lower cut-off from the training phase RTs in order to compensate for the prep time (i.e., target ISI = 1000ms but ~100ms prep time - so set actually ISI to 900ms to approximate a 1000ms ISI).

All the best,
Marton

UPDATE - I have managed to tighten up the timing for the DT only version of the experiment on on one our testing PCs. However when implementing this version of the DT into the full experiment, the presentation timing for the dual task blow-out massively (by ~1000ms), and I am not sure why. Can post full version of exp if necessary.

eduard

I pinged Roelof. I hope he'll get back to you soon

Eudard

Roelof

there's a reply in the original thread, thank Eduard for the heads up