Measuring Visual angle of stimulus in Psychopy using Builder view

[mithilesh tiwari]

Hello everyone,

I am novice user of Psychopy 1.79.01 on my laptop running Windows 8. I wanted to build an experiment in which some English alphabets will appear either in left visual field or right visual field at certain visual angle (let visual angle is equal to 3 degree horizontal and 2 degree vertical). How accurately may I suspend stimulus by creating Microsoft Excel file list of stimulus and giving Xpos and Ypos columns corresponding visual angles. Since, As I know, visual angle is dependent upon the distance from participant is looking at screen, screen distance and screen resolution. Screen resolution and screen size is fixed and what can vary is the distance between screen and participant.

Therefore, I want to exactly know how much distance should I keep between screen and participants?   

[Jonas Lindeløv]

See http://www.psychopy.org/general/units.html#degrees-of-visual-angle

Basically, you set the position (and size etc.) using the unit "deg". To set the distance to subject and monitor dimensions, use monitor center. There's an icon for that.

Notice that a visual.TextStim(height=2, units='deg') is not neccessarily 2 degrees high as the height is of the "box" surrounding the text. But you can adjust the height until the physical size is correct. Here, multiplying the desired height by 1.6 makes it approximately right.

Best,

Jonas