Dual task timing
I have used opensesame to build a free recall experiment where participants see lists of words that they attempt to verbally recall either under a serial RT dual task or no dual task conditions. The dual task is one in which one of four coloured dots appears randomly in 3/4 possible positions in horizontal frame (dot can not appear in the position that is congruent with the relevant response key).
At the moment this is achieved via a 4 colour x 3 position loop that contains the dual task sequence. The dual sequence primarily consists of 4 sequences that are executed conditionally (one of each colour dot), with each sequence consisting of a sketch pad item and a response logger. The sketchpad for each coloured dot contains conditional statements that are executed in order to display 3 each coloured dot across all possible positions each coloured dot can appear.
The issue I am having is that I am unable to maintain the presentation timing for the dots (atm being set via the response collection timeout in each dot sequence) that is being calibrated via response times for the task taken from a training phase. There appears to be an approx. 300ms preparation time associated with each sketchpad (i.e., coloured dot) which results in a presentation rate of 1000ms per dot actually taking 1300ms. This problematic for a number of reasons -
1) the presentation is not appropriately calibrated to training phase performance (slower than it should be); and
2) the length of the dual task is based on the number of times the DT sequence needs to be called in order to approximate a 30 second (auditory) free recall window. On the basis of a 1000ms presentation rate, the experiments calls the DT sequence 30 times. However due to the preparation time, the presentation rate is actually around 1300ms which results in a the free recall window lasting ~40s (not the intended 30s).
I tried a couple of ways to fix this issue:
- manually adjusting the presentation rate and/or number of times DT sequence is called. While I was able to approximate a 30s window, the response times recorded are not correct i.e., getting a presentation rate of 1000ms (i.e, 30s recall window = DT sequence x 30) via setting response time out to 600 + 400ms preparation time records response time outs as 600ms (rather than 1000ms).
- due the lack of preparation time associated with loops, replacing the dot sequences with loops. This actually made performance worse - 30 x 1000ms trials taking >60s.
- inserting an advanced timing delay into the DT sequence to take into account the preparation time for the each sketchpad. However, adding a 400ms advanced delay simply increased the presentation rate by 400ms (was under the impression that the next sketchpad could be prepared during the advanced delay?).
Any suggestions on how best to maintain timing this particularly kind of dual task? In the advanced tutorial you demonstrate how to use the prepare/run strat to prepare all stimuli for the attentional blink exp in advanced (i.e., having a list of canvas items that is iterated through). However, the stimuli for that experiment were single letters so not sure how easily my dual task stimulus could be prepared in a similar way.
All the best,