Running independent loops simultaneously with sound and visual stimuli

Great! Thanks for the detailed description - I think it should all work OK.

I suspect the slowness issue is caused by lots and lots of print statements, because it was printing a new statement every time it registered that the mouse button was in a down state (not just the action of pressing it). You might be able to resolve both it and the double-click issue by putting some code like this outside of the trial loop:

m_known_down = any(mouse.getPressed())

last_click = -1.0
double_click_range = 0.3

and then replace the mouse handling code with something like:

    if any(mouse.getPressed()):
        if not m_known_down:
            m_known_down = True
            m_click_time = clock.getTime()
            if (m_click_time - last_click) < double_click_range:
                print "Double click registered"
            else:
                print "Mouse click registered"
            last_click = m_click_time
    else:
        m_known_down = False