Hi, I have a question on how to best programm a random selection of pictures from one pool into separate picture pools that starts at the beginning of a trial. I have a pool of 16 pictures and at the beginning of an experiment I want them to be randomly assigned into 4 separate pools: 4 pictures per pool. These picturs will then be drawn at and presented in 4 different within design conditions (reperesnted by trials), where also other characteristics are counterbalanced (e.g. picture position). I tried to accomplish it by creating a central list of 16 pictures and programm a very first trial of the experiment so that it randomly draws 4 pictures into one list and erases them from the central list and the same should happen for the next 3 lists. Then the lists are used as a “selection” reference in picture elements, as lists cannot be really used as “item” elements in trials etc. However, it does not seem to work well, I keep getting these errors:“Error evaluating ´100´/: Unknown error.”“Unable to initialze <picture xy> item number 0. Verify the item exists and its correctly defined.”Any ideas? Thanks! Here is my script:<item all_central>/1=picture1/2=picture2/.../16=picture16</item><picture all_central>/ items = all_center/select = noreplace/ position = (50, 50)/size = (550,600)</picture><list all_central>/ items= (all_central)</list><list congruent_a>/ items= (list.all_central)/poolsize= 4/selectionmode = random</list><trial remove1>/ ontrialbeginning= [list.all_central.removeitem(list.congruent_a);]/timeout = 1</trial><list incongruent_a>/ items= (list.all_central)/poolsize= 4/selectionmode = random</list><trial remove2>/ ontrialend= [list.all_central.removeitem(list.incongruent_a);]/timeout = 1</trial><list congruent_b>/ items= (list.all_central)/poolsize= 4/selectionmode = random</list><trial remove3>/ ontrialend= [list.all_central.removeitem(list.congruent_b);]/timeout = 1</trial><list incongruent_b>/ items= (list.all_central)/poolsize= 4/selectionmode = random</list><picture xyz_left_congruent_a>/select = list.congruent_a/ position = (25, 50)/size = (250,300)</picture><picture xyz_left_congruent_b>/select = list.congruent_b/ position = (25, 50)/size = (250,300)</picture><picture xyz_right_congruent_a> /select = list.congruent_a/ position = (75, 50)/size = (250,300)</picture><picture xyz_right_congruent_b> /select = list.congruent_b/ position = (75, 50)/size = (250,300)</picture><picture xyz_left_incongruent_a>/select = list.incongruent_a/ position = (25, 50)/size = (250,300)</picture>etc..trial example:<trial l_congruent_left_face_a>/inputdevice=mouse/validresponse = ("liking_button","disliking_button")/stimulustimes = [500=fixation_cross; 1100=face_center; 1100=xyz_left_congruent_a; 2700=facegaze_left; 3500 = x_button, y_button]</trial>