[DMDX] Re: Progressive Demasking 
>   You'll certainly get display errors on slower machines and given that I 
> recently fixed a problem with DMDX wasting time while looping in large 
> item files it's more likely to have happened in the past but any errors 
> that script makes (assuming it gets fixed as I mentioned) would leave the 
> mask up for longer than a fixed duty cycle would dictate, not the 
> stimulus.  Unless of course the machine is not up to displaying the raw 
> item without the looping...

I'll update things at some point and have a play and see if the problem 
still occurs.

>   Was thinking about progressive de-masking this morning and realized 
> that the first clockon has to be the one that is left in the item file 
> and the subject timeout has to be set to whatever 30 ticks evaluates 
> to.  The problem with these kinds of displays is that while DMDX can do 
> quite sophisticated things with the display across items you can't gather 
> responses across items.  So the clock must be turned on when the mask is 
> displayed to catch any response made to the previous iteration of the 
> loop and the response timeout has to be set so that the duration of the 
> mask is not lengthened.  It still means there's a couple of ticks where a 
> response could be made that DMDX won't see, or at least that it will 
> probably not see till the beginning of th

If things work I will have play and try and work out what proportion 
responses this problem typically affects, cos I would like to use PDM at 
some point.  I'll post results when/if I get them.

- Mike

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*** Note New Extension - 335 ***

Mike Ford
MRC Cognition & Brain Sciences Unit
15 Chaucer Rd, Cambridge, CB2 2EF, UK.
Tel:   +44 (0)1223 355294 ext 311     Fax:   +44 (0)1223 359062

http://www.mrc-cbu.cam.ac.uk/personal/mike.ford
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