Millisecond Forums

Hello,

I'm starting a new post here because my previous post was difficult to navigate as a result of my copy/pasting.

I am using a Tobii X2-60 eye tracker and have a question about recording markers at stimulus onset and offset. I think my onset marker method is working as desired but the offset marker has an issue. Currently, my trial runs like this: (it is just a training trial at the beginning of my experiment)

<trial trainingsession>
/ ontrialbegin = [
values.correcttrain = list.hpos.nextvalue;
values.distractortrain = list.hpos.nextvalue;
values.trainTitem = list.trainingitemsT.nextindex;
values.trainFitem = list.trainingitemsF.nextindex;
]
/ ontrialbegin = [
if (values.correcttrain == 30%) values.target = parameters.responsekeyleft else values.target = parameters.responsekeyright;
]
/ stimulustimes = [0= clearscreen; 400=mypicturetrainT, mypicturetrainF, stimOnsetMarker; 450=correctopiontrain, distractoroptiontrain; 1200=mysoundtrain; 1300=stimOffsetMarker]
/ inputdevice = keyboard
/ datastreams = eyetracker
/ validresponse = (parameters.responsekeyleft, parameters.responsekeyright)
/ correctresponse = (values.target)
/ response = correct
/ errormessage = true(errortxt, 500)
/ correctmessage = true(traincorrect, 800)
/ recorddata = true

The above is with onset and offset markers set as follows earlier in the script

/*this marker sends value "1" to signal onset of stimulus
<port stimOnsetMarker>
/port = eyetracker
/items = (1)
</port>
/*this marker sends value "0" to signal offset of stimulus
<port stimOffsetMarker>
/port = eyetracker
/items = (0)

I was hoping to end up with regular intervals (e.g onset and offset markers should be present in my data for constant intervals of time - roughly 900ms (1300-400)) but this is not the result I am obtaining. I assume this is because a response can be made anytime during the trial (even before the sound stimuli...although that is not anticipated)... In such a case, I am unsure as to the timing of the offsetmarker. Currently, when testing this myself I get onset time intervals (for 10 items) ranging from 600ms to 891ms. Am I correct in assuming this is due to my response timing? (also, I understand that some minor fluctuation in times is the result of various margins of error (latencies) and their subsequent stackup - so far, this appears to account for very roughly 10ms or so)

1. Maybe I should be setting the offset marker just before the sound stimulus is presented. e.g. 1199=stimOffsetMarker

2. Or, thinking from a different perspective, is it possible to set the offsetmarker to coincide with the keyboard response timing?

3. And, one additional question - is it possible to get stimulus item data in the eyetracker data stream? For example, a column appearing in the eyetracker data file with the heading stimulusitem that lists the stimulus present....or maybe sending this much data to the eyetracker slow everything down...?
Regards

Jason