Given my 8 bits of color depth, I guess that the minimal contrast that I can display is 1/2^8, which is about 0.004, but I realized that when I set up the contrast to a value much smaller than that (e.g. .0000001), I still can see the stimulus, which means that something is presented. Shouldn’t such a small value be rounded to zero and nothing being presented?
Below some code in which I can see the stimulus despite the small contrast:
from psychopy import core, visual, event win = visual.Window([400, 400.0], allowGUI=False) gabor = visual.GratingStim(win,size=1.0, sf=8) trialClock = core.Clock() while trialClock.getTime() < 20: gabor.contrast=.0000001 gabor.phase += 0.01 gabor.draw() # handle key presses each frame if event.getKeys(keyList=['escape', 'q']): win.close() core.quit() win.flip() win.close() core.quit()