Set up a <values> entry
/ correct = 0
and set that value to 0 (incorrect) if the page times out (latency >= 10000).
Log that value to the data file.
#1: You cannot set a trial's correct-property. The correct-property is read-only.
/ ontrialend = [if (slider.stim_slider1.response == "50" && slider.stim_slider2.response == "50" && surveypage.rating.latency < 10000)
surveypage.rating.correct == true]
#2: Even if it were possible to set it, you'd be using the wrong operator. == is a logical comparison operator, the assignment operator is =.