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ViewingDistanceScreenSizePixels-per-degreeMeasurements from November 2008 (Measurements made by Andre and Ghislaine around the end of November 2008. Information sent by Ed Hubbard via e-mail on 13 Feb 2009) From: Edward Hubbard <edhubbard AT gmail.com> Date: Fri, Mar 13, 2009 at 3:40 PM Subject: Re: [unicog] pixels into degrees in 3T Hi Marcin and all, Andre and I looked into this for our study, and took two separate (converging) measures of degrees per pixel for the paper that is currently under review at Science. Andre used the size of the large circle, which was 6.10158 degrees, and was 240 pixels, to come up with a measure of about 0.0254 degrees per pixel. We then did the same thing for one of my saccade tasks, where the displacement was 5.03375 degrees, and was 192 pixels, to come up with a measure of 0.0262 degrees per pixel. So, as you can see the two measures are the same to within a small measurement error. If you like you can simply take the mean and use that as your starting point. André’s images 6.10158° / 240 = 0.02542325° per pixel Ed's saccades: 5.03375° / 192 = 0.0262° per pixel In both cases, this is with the newer projector (installed late spring last year), with the resolution set at 1024 x 768. I don't remember the exact distances, and so on, but perhaps Andre still has those notes on his computer somewhere. Cheers, Ed Information from Sepideh measured on 09. March 2009 I only know that the total width of the projection is visible to the subject in the Neurospin 3T scanner. The (center point of the) mirror of the subject is at exactly 1m distance and the width of the projection on the projection screen is 41.5 cm. This results in a total visual angle of 41 degrees (arctang(20.75cm/100cm) x2). The visual angle of the height is considerably smaller, but I didn't measure it. Best, sepideh |