Keeping fixation: Inter stim duration difficulties

[Laura Forde]

Hi, 

I have two experiments that require stimuli to be presented at different inter-stimulus intervals (IVI) and at three different locations on the screen. I have been able to create these, however, am struggling to find a way to ensure that the fixation cross stays on screen at all times. The way one is currently configured is to have a text display (pre-slide object in the session procedure timeline) with the fixation cross and its duration hyperlinked to the InterStimDuration attribute that I created in the list. I also have an attribute for space on screen (left, right, middle) and the respective stimuli- these are both hyperlinked to from the slide sub-object. In practice, this sees the cross fixation come up for the ISI, the stimuli then appear at their respective location and RT and accuracy are logged etc. My difficulty is that I want the fixation cross not to disappear when the stimuli are on screen. I have tried adding a cross to the object slide but this results in at worst a cross that jumps on the page and at best a flicker as it transitions from text display to slide object.

Is there a way of having this permanent fixation and having the stimuli presented at different locations to predetermined intervals?

Also, the second experiment is similar, though in this instance I am having the ISI be randomly drawn from between 100,4000 and its hyperlinked to from the fixation text display in inline, as follows:

Dim duration As Integer

duration= random(100,4000)

c.SetAttrib "FixDuration", ""

c.SetAttrib "FixDuration", duration

I again would like to have the fixation cross always present. 

Please advise!

Laura

[David McFarlane]

Laura,

A few thoughts ...

1) Make all your stimuli as Slide objects, including your fixation, and
add the cross as a sub-object in the appropriate place on each Slide.
This should keep the cross always in the same location.

2) If your actual stimuli never overlap with the cross, then just put
the cross up once at the start, then set the Width and Height properties
of your sub-stimuli so that they never erase that cross.

3) Set the BackStyle of your main stimulus & sub-stimuli to
"transparent", so that once again you can just leave up the original
fixation cross.

Please write back with whatever you end up doing.

---------------
David McFarlane
E-Prime training online:
http://psychology.msu.edu/Workshops_Courses/eprime.aspx
Twitter: @EPrimeMaster (https://twitter.com/EPrimeMaster)