Jitter ITI Code Error - Builder

Builder
1

If this template helps then use it. If not then just delete and start from scratch.

OS (e.g. Win10): Win10
PsychoPy version (e.g. 2024.2.4 Py 3.8): 2025.1.1
Standard Standalone Installation? (y/n) If not then what?: y
Do you want it to also run online? (y/n) n

I am trying to add a jittered inter-trial interval to my experiment in builder. I have used some code from another post on this forum, and there is no syntax error in the code itself, but when I try to pilot the study I get a TypeError saying ‘can’t multiply sequence by non-int type ‘float’’.

jitter = [random() * [500 + (486)]] #add jitter
jitter = round(jitter, 1) #round to 1dp
thisExp.addData('jitter', jitter) # add 'jitter'column to data spreadsheet

This is the code I have used, in a routine before my main task routine. Any help on how to fix this would be much appreciated!

2

random() returns a number between 0 and 1. What would you expect jitter to look like if random() returned 0.5? Are you using square brackets (which denote a list) when you mean parentheses?

3

Thank you for your response! I didn’t realise random only worked between 0 and 1, I thought it returned a random float (as opposed to randint()). If it returned 0.5 I would assume a jitter of 493ms.

You were right about the square brackets - using parentheses stops the error, but there is no jitter occuring.

4

Is the jitter value now being saved to the data file?

It looks like your jitter is in ms. Are you converting to seconds when using?

Also, I would round to the nearest ms, since screen refresh means you probably can’t be more accurate that 16ms anyway.

5

Hello @daisy.s

the code

randDurFix = random() * .1 + .6

returns a random number between 0.6 and 0.699… seconds.

Best wishes Jens

6

There is a jitter column with one value at the top, but no jitter for the rest of the trials - I am aiming to have a different interval for each trial but there is no data in the rest of the boxes.

I will keep it in ms, and round to the nearest ms as you suggest.

7

Hi @JensBoelte , thank you for your reply!

I’m afraid this code gives the same result as others I have tried - one value at the top of the ‘jitter’ column, but no data for the rest.

8

The code should be in a Begin Routine tab if you want to change it every iteration. It sounds like you either have it in Begin Experiment or in a routine outside your trials loop.

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