stimulus size in degrees of visual angle

[David McFarlane]

Maggie,

E-Prime displays work in units of pixels, or 
%.  You will have to convert that to visual 
angle.  To do that you will have to know the 
physical dimensions of your screen, and the 
distance from the observer to the screen.  From 
there it is just a little bit of math, which you 
can find in the Wikipedia article on "Visual 
angle".  You should be able to take it from there.

(Aside to PsychoPy users:  Yes, PsychoPy, unlike 
E-Prime, will work directly in units of visual 
angle, after you tell it the measurements mentioned above.)

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

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At 10/17/2013 09:26 AM Thursday, Maggie wrote:
>Hello,
>
>I'm just starting to learn how to use eprime and 
>I've run into some trouble with the stimulus 
>size. I need to place a geometric shape (i.e. 
>triangle or square) above the fixation point, 
>and it needs to be 3.8° x 3.8° in size. How to I 
>convert this into pixels exactly? I'm assuming 
>the size (height and width) in properties are in pixels too, right?
>
>Many thanks,
>Maggie

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