[open] Inhibition Experiment with Variable Stimuli Presentations

caamitchell11

Hello!

I am new to using OpenSesame and have spent quite a bit of time trying to get used to it/reading the tutorials. I thought I understood it enough to begin constructing my experiment, but I think I am just confusing myself!

In a nut shell, this is my experiment:

• Stimuli = 48 pictures
• Structure = 2 'runs' or blocks
• Trials = The sequential presentation of 85 pictures in each run --> initial presentation of each of the 48 pictures and then 37 repetitions of some of the pictures (22 presented a second time, and 15 presented for a third time; randomized). The initial 48 trials are distractor trials, and the repetition trials are the target trials.The pictures selected as targets are changed in the second run

In each run the subjects are asked to indicated whether they saw the picture being presented within the current run ("Yes" or "No").

I aim to record the number of hits (correct identifications), false alarms (incorrectly selecting a distractor), and RT for responses to targets (hits) and distractions (correct rejections).

I was wondering how I would organise the visual stimuli within the block - would I need loops or just blocks? Would I require two different sequences (one for distractors and one for target trials)? I am also not sure how to set it up so that I obtain the correct dependent variable data.

Apologies if it may be quite simple - I have been looking at it for too long!
Thanks in advance.

eduard

Hi,

The easiest implementation that comes to my mind is based on inline_scripts. In those, you can define the list that you want to present in each round in the beginning of a block, so that in the actual loop you only have to access the right index. The structure of your experiment could then look like this:
First, you use add a loop-sequence structure to your experiment. In this one, you define an inline_script, in which you set all the lists you need, and another loop-sequence structure (the loop for the trials), in which you put a sketchpad (stimulus presentation), a keyboard_response (response collection) and a logger (write everything to file). How to use the last three items, you probably learned from the tutorials. What to put in the inline_script follows here:

import random

# put all the image filenames in a list and make sure the files are in the 
# file pool
all_pictures = ['pic1.JPG','pic2.JPG',...]
#set parameters
no_images = 48
no_1repeat = 22
no_2repeat = 15

# a list with 22 repeated images selected for the list created above
one_rep = random.sample(all_pictures,no_1repeat)

# a list with 15 repeated images selected for the first repetition list
two_rep = random.sample(one_rep,no_2repeat)

var.all_stim = all_pictures + one_rep + two_rep
random.shuffle(var.all_stim)

The variable var.all_stim is now a list with 85 randomized images names. In your trial_sequence you can access one image by one image from this list.

I hope this helps.

Good luck,

Eduard

caamitchell11

Thanks Eduard!

Your response was incredibly helpful. I will try this approach :-)

Thanks again.

Claire