How do I randomly generate numbers with a certain amount of probability?

Hi there,

Brand new to programming so sorry if this is a dumb question.

I have two folders with twenty-four images each, one folder contains emotional images and the other folder contains non-emotional images. The images are to be displayed on the left and right side of the screen under four conditions:

Non-emotional on the left - Emotional on the right for 6 trials

Emotional on the left - Non-emotional on the right for 6 trials

Non-emotional on the left - Non-emotional on the right for 6 trials

Emotional on the left - Emotional on the right for 6 trials

I figure I can do something like this using if statements, for loops, and randomly generating 4 different integers. The problem is if I do this by generating a random integer from 1-4, I want to make sure no integer is generated more than 6 times, because that would mean that the condition occurs for more than 6 trials. How can I do this?

Alternatively, is there a better way to do what I want to do?

Thanks in advance,

[Image Analyst]

Have you tried dir(), randperm(), and imshow()?

Have you seen the FAQ?

Answer 1

[John D'Errico]

As is often the case, I would suggest you are overthinking this.

You have a sequence of 24 pairs of images to be shown. There will be 6 trials each for each combination. (At each trial, I assume you will randomly choose a pair of images from each folder. But that is not relevant at this point.)

So, consider what this matrix would indicate, assuming that a 1 indicates a non-emotional picture, and 2 indicates a choice from the set of emotional images.

trials = repmat([1 2;2 1;1 1;2 2],6,1);
trials = trials(randperm(24),:)

trials =
     2     2
     2     1
     2     1
     1     2
     2     2
     2     1
     1     2
...

Each combination occurs exactly 6 times, in randomly permuted order.