[solved] Setting Up an Experiment

Vikki

Hello,

Having gone through the tutorial, I am still at a loss how to actually set up my experiment. I shall try and explain how I want to do it and any advice on how to go about setting it up would be very gratefully received:

Ok, so I have 30 backgrounds each a different scene (e.g. a picture of a living room). I also have images of 12 individual people, however, each image has three versions: one in which only contains the head of the person (Face-only trials), one in which only contains the body of the person (Body-only trials) and one in which contains the full body of the person (i.e. face and body combined –Full-body trials).

Now what I want to happen in each trial is that the background will be shown with a person (or part of a person) within the picture, at varying locations (i.e. left, centre or right). Is it possible to get opensesame to randomly pick a background and randomly pick a person stimulus and superimpose the image of the person (or part of a person) within the background image, at one of the three locations?

I want the backgrounds to be displayed an equal number of times within the experiment. Additionally, I also want the each person to be shown an equal number of times within the experiment. Furthermore and most importantly, I also want there to be equal numbers of Face-only, Body-only and Full-Body trials within the experiment.

I want this to be random for each participant and I don’t want hundreds of trials, if there is a large volume of trials a break half way through the trials would be ideal. How do I go about setting this up in opensesame? I'm sorry for all the questions!

Thank you so much for your help,

Vikki

sebastiaan

Hi Vikki,

As a first step, don't worry about the background and the location of the person. Just focus on selecting the proper person image.

Step 1 First, give convenient names to all your person images. Like so:

1-face.png
1-body.png
1-full.png
...
12-face.png
12-body.png
12-full.png

Step 2 Now add two variables to the block loop, to define the person nr. (person_nr) and the body part (body_part). Please see the tutorial for how to do this. You should end up with a loop table like this:

person_nr body_part
1  face
1  body
1  full
...
12 face
12 body
12 full

Step 3 Now add a sketchpad to the trial sequence and add some person image to some location on the sketchpad. Now, right click on the image and select edit. Change the script so that the two variables are used to select the correct person image:

draw image 0.0 0.0 "[person_nr]-[body_part].png" scale=1.0 center=1 show_if="always"

Click ok to accept.

Now you should already have an important part of your experiment in place! Does this work for you?

Cheers,
Sebastiaan

Vikki

Thank you so much,

I will let you know how I get on! I'm sure I will have another millions questions :-)

Thanks again,

Vikki