Skipped TextDisplay retains previous trial's .RT etc.

[David Vinson]

Dear E-Prime group,

I am working on an E-Prime 2.0 experiment, with a procedure that 
contains one or two response objects - display of the second one only 
happens on some trials. The problem is that "old" trial data are 
retained for those trials for which the second response is skipped. I'm 
sure there's a simple solution but I've thought myself into a corner on 
this one!

Here is a brief description of a toy version of the experiment which 
exhibits the same problem:
-----------------------------------------------------------------------------------------------
We have a list Object which calls a single procedure including the 
following main elements:

1. TextDisplay "Displayed every time" which appears on every trial, with 
standard data logging.

2. Inline "Check for skip" - 40% of the time the second textdisplay will 
not appear, instead setting a "Skipped" variable and skipping to a label 
after the second text display.

3. TextDisplay "Displayed sometimes", with standard data logging.

4. Label "Skip second",

5. Inline "Cleanup" which uses c.SetAttrib to set DisplayedSometimes.RT 
to -99 (and other such attributes/values) only if the Skipped variable 
is set.

-----------------------------------------------------------------------------------------------
When the experiment runs, this works as desired, skipping the second 
text display approx 40% of the time.

Our problem is in the data file. Assume that DisplayedSometimes occurred 
on trial N, thus generating real RTs etc for that trial, and that 
DisplayedSometimes was skipped on trial N+1 (and thus 
DisplayedSometimes.RT should be -99). Instead, we find that the same 
values are logged from the last time they were collected (e.g. if .RT 
was 555 on trial N, it will appear as 555 for trial N+1, and so on until 
DisplayedSometimes occurs again).

If we add a c.Log to the "Cleanup" inline, this creates two entries for 
trial N+1 in the data file. The first entry contains our desired values 
(.RT of -99), The second entry, however, contains values from trial N, 
e.g. .RT of 555).

Is there any way to clear/flush the previous trial data from objects 
like DisplayedSometimes in the example here? (or otherwise correctly 
assign NULL or some identifiable "skipped" value like the example of .RT 
= -99 to those trials)?

We have considered the possibility of calling two different Procedures 
(one with a single TextDisplay and the other with both), but haven't 
found a suitable solution as in our actual experiment, the decision to 
skip or not is partially contingent upon the response made to the first.

I'd be grateful for any advice - can supply a toy version of the 
experiment if my verbal description is confusing!

(I have submitted a request to PST support but thought I would risk a 
concurrent submission to the group after seeing the "We are currently 
experiencing a large volume of requests..." message on the support site!).


Thanks,
David

-- 
David Vinson, Ph.D.
Postdoctoral Researcher
Deafness, Cognition and Language Research Centre (DCAL)
University College London
49 Gordon Square, London, WC1H 0PD
Tel +44 (0)20 7679 8688
d.vinson at ucl.ac.uk


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