problem with summation object

[Rob Hester]

To the mailing list,

I have been successfully using the summation object script (available on 
the e-prime website) to collect and average the number of correct responses 
from 100 trials, but I've run into a problem when I changed the stimulus 
timing properties of the task.
I've have a flanker task setup so that the stimulus display object is 
presented for 100ms and then changes to a second stimulus display object (a 
blank screen) while it waits for the participants response. I have the 
stimulus display object 1 response properties configured so that it runs 
for 100ms (cumulative timing with 100ms) with the response input time limit 
set to 'infinite' and end action set to 'terminate'. Stimulus display 
object 2 does not accept responses, but is set to an infinite time limit. 
The summation object in line script is placed after Stimulus display object 
2 (although it doesn't matter if I move it to after SDO1), and reads:

'The AddObservation command adds the ACC value of object
'StimulusPresentation to the Summation object, OverallAcc.
OverallAcc.AddObservation c.GetAttrib ("stimulus.ACC")

'The Debug.Print command prints the mean value of the Summation
'object, OverallAcc, in the Output window.
Debug.Print OverallAcc.Mean

'The OverallACC attribute adds the running calculation of overall
'accuracy to the data file at the trial level.
c.SetAttrib "OverallAcc", OverallAcc.Mean


How does having the second display object interfere with this script, 
because removing makes the summation work perfectly? Anyone got a suggestion?

Cheers
Rob



Dr Rob Hester
Research Fellow
Department of Psychology
University of Melbourne
Victoria 3010
Australia
Tel: +61 3 83443684
Fax: +61 3 9347 6618
hesterr at unimelb.edu.au