visual angle

1
Dear all,
My question might sound quite naive, but, I present the stimuli in the center of a 21 inch LCD monitor which is 90 cm away from the subject. How can I explicitly describe the stimulus location in terms of vertical and horizontal degrees, what is the algorithm or calculation for that?
best,
Sibel
2
For your setup, this will work fine. Do note that angular distance does not scale linearly with distance on the screen once you get out to above about 40 degree, then things get more complicated in that you have to calculate each directly by adapting Alan's formulae


On Thu, Jun 19, 2014 at 4:40 PM, Alan Robinson arcogsci@... [PSYCHTOOLBOX] <PSYCHTOOLBOX@yahoogroups.com> wrote:


as matlab code:

%width and dist measurements fall out so just be sure to use the same
%units for both (currently, inches)
hRes = 1920; hSize = 41; vDist = 57; % LG TV 46 pix per deg

degPerPix = 2*atand( (hSize/hRes) / (2*vDist))
pixPerDeg = 1/degPerPix


On Thu, Jun 19, 2014 at 5:57 AM, Sibel Ozer sibelozer.ege@... [PSYCHTOOLBOX] <PSYCHTOOLBOX@yahoogroups.com> wrote:

Dear all,
My question might sound quite naive, but, I present the stimuli in the center of a 21 inch LCD monitor which is 90 cm away from the subject. How can I explicitly describe the stimulus location in terms of vertical and horizontal degrees, what is the algorithm or calculation for that?
best,
Sibel