# Randomization of grating

Hi! I’m new in PsychoPy/python. I try to create a match-to-sample task with gratings (horizontal & vertical). I created circular gratings (components > stimuli > grating) and I organized my experiment into two routine: the first with one grating and the second with two gratings (position (x,y): 0,5 and -5,0 respectively). Nevertheless, I am facing two problems:

1. When I run it, the first grating is displayed and then it stops
2. How can I randomize the position of two gratings in the second routine? [i.e. I wanna create a block of 6 trials consisting of two routine. The first with one grating (e.g. horizontal grating) and the second with two gratings (one horizontal and one vertical) with random position]
Do you have any idea? Thank you in advance!

Hello

insert a code-component in top row of the routine in which you display your gratings. In the Begin Experiment tab, insert

``````xPos = [-0.25,0.25]
``````

to initialize the list (not when running locally)

In the Begin routine tab, insert

``````xPos = [-0.25,0.25]
shuffle(xPos)
xPosGrat1 = xPos.pop()
xPosGrat2 = xPos.pop()
``````

Chose the Layout tab of the first grating property and specify the location.

``````(xPosGrat1, 0)
``````

Set this property to set every repeat.

Do the sam for the second grating. This time, however, specify

``````(xPosGrat2,0)
``````

You might want to save the positions by adding the following two lines to the “Beginn routine” tab.

``````thisExp.addData("xPosGrat1", xPosGrat1)