[DMDX] deadline procedure Hi,

I was wondering if someone could assist me with the following problem: I 
would like to set up an experiment in which a target stimulus is 
presented for a fixed amount of time, say, 2000 ms. At a fixed time 
interval into the trial, say 500 ms, I would like to have DMDX do the 
following: if there was a response prior to the 500 ms deadline, I want 
DMDX to do nothing, but if no response occurred by that time, I would 
like to play a sound, while still awaiting a response until the timeout. 
In other words, the feedback regarding whether or not participants 
responded within the deadline interval should occur *within* an ongoing 
trial.

So far I haven't been able to find a solution to this problem. It is 
relatively straightforward to have DMDX perform a conditional branch 
*after* a response occurred, with the LastRT keyword in combination with 
a bicLE etc. statement. But here I would like to have the deadline sound 
presented only if *no* response was made by a certain time. One solution 
that I thought of was to schedule an event, at exactly 500 ms, that 
looks at LastRT, and performs a conditional branch. But  to my knowledge 
LastRT contains the last RT collected within the experiment, so DMDX 
cannot distinguish between RTs collected on the current, and on the 
previous, trial. Is there a way to reset LastRT between trials? If I 
could set it to zero at the beginning of each trial, I could then at 500 
ms state: if LastRT is not 0, then (a response must have occurred within 
the current trials, and therefore) do nothing, otherwise play the sound.

Any help would be appreciated!

Markus


Markus Damian
University of Bristol
Department of Experimental Psychology
8 Woodland Road, 5D5
Bristol BS8 1TN
United Kingdom



