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()