Hello again!
I got the lower window exchange to work. That alone taught me some things about global variables and how to think about those TexQuads. Now on to the next problem: Exchanging the picture in the lower window 7 out of 10 times with one picture and 3 times with another (randomly).
I tried the list strategy, as suggested by Erikvdb, I've consulted all my resources, and I managed to implement it. However, the problem is that sometimes it shows the picture C 3 random times (as it should), other times, only 1 or 2 times.
 Almost as if it's randomly picking from the list 10 times. However, I want it to go through the entire list once. I am wondering if my list implementation is correct? Maybe I should not put several identical elements in a list? Or it's a problem regarding the implementation inside the "while loop"
I tried to simplify the code and create this as a separate script with the simplest form of the issue, as suggested by Jeff. Rather than code debugging I am hoping that someone might link me to a relevant example of a list within a loop. Obviously I am lacking the logic behind it especially when things get nested.
	Code:
	## Import Vizard modules ##
import viz 																														
import viztask							
import random							
#Start Vizard:															
viz.go()
## STIMULI ##
#pictures
pictureA = viz.add('picA.jpg')
default = viz.add('default.png')
#sound
cue = viz.addAudio('dong.wav')
#list (7 times picture B and 3 times picture C)
pictureList = ['picB.png', 'picB.png', 'picB.png', 'picB.png', 'picB.png', 'picB.png', 'picC.png', 'picC.png', 'picC.png']
#Make a screen window:
screen1 = viz.addTexQuad(size=0.5)            
screen1.setPosition([0,2.1,1.3])
screen1.setSize([0.4, 0.4])
#Make a second screen window:
screen2 = viz.addTexQuad(size=0.5)            
screen2.setPosition([0,1.6,1.3])
screen2.setSize([0.4, 0.4])
## TASK##
def task():
	screen1.texture(pictureA)
	screen2.texture(default)
	def playCueLoop():  # default picture is shown in lower window + 10 times, at randomly intersperced intervals, a sound beep plays & each time that happens, the lower window replaces the default picture randomly with 7 times picB and 3 times pic C
		count = 0
		while count < 10:
			count += 1
			cue.play()
			pictureIndex = 0
			random.shuffle(pictureList)
			picture = viz.add(pictureList[pictureIndex])
			screen2.texture(picture)
			pictureIndex += 1
			yield viztask.waitTime(0.5)
			screen2.texture(default)
			yield viztask.waitTime(0)
			yield viztask.waitTime(random.randrange(1,4))	
	viztask.schedule (playCueLoop())
viztask.schedule(task())
 My only resource is a huge code with one list example (but there is no loop) - this is just a snippet:
	Code:
	photoList = ['A1.jpg','A2.jpg','A3.jpg','A4.jpg','A5.jpg','A6.jpg','A7.jpg','A8.jpg','A9.jpg','A10.jpg']
random.shuffle(photoList)
photo = viz.add('Pictures\\' + photoList[photoIndex])
photoFrame.texture(photo)
photoIndex += 1
 I would be very greatful for any help or pointers!
P.S. I know Erikvdb suggested in another thread to stop the sound as well, however I left that out for now, to simplify the code