Loop: go back an iteration

Builder
1

OS (e.g. Win10): MacOS
PsychoPy version (e.g. 1.84.x): v2024.2.2
Standard Standalone? (y/n) If not then what?: y

I want the participant to have the ability to go back an iteration and redo the answer if they want. How do I go back an iteration, programatically or otherwise with a back button.

2

The way I do this is with concentric loops. The inner loop uses the selected rows function to select a single row from the spreadsheet, e.g. useRows = str(Idx) + ‘:’ + str(Idx+1) though useRows = [Idx] should also work. The outer loop repeats with no spreadsheet for a large number of repetitions until the value of Idx is too high and then ends with outerLoopName.finished = True

However, I believe there are timing implications with this approach since the timing for the first iteration of a loop seems to be less consistent than later iterations.

3

Hmm, I understand the solution a bit, but it’s too complicated. Is there no way to programmatically control the loop iterations?

4

Actually, as of 2024.2.0 there is.

trials.rewindTrials() or trials.rewindTrials(1) will repeat the same trial

trials.rewindTrials(2) will rewind one trial (but a bug means that it can’t get back to the first trial)

trials.skipTrials() or trials.skipTrials(1) will skip a trial

trials.skipTrials(2) will skip two trials

The above code is based on a loop called trials

These functions don’t yet work online.

This behaviour will probably change in 2025 – I just tried my demo in a pre-release version and in that one you need to use trials.rewindTrials(0) to repeat a trial (no change in row number) and trials.skipTrials(2) to skip a trial (+2 to row number).

5

Hi @wakecarter, Thanks!!! I just checked the api and it’s exactly what I’m looking for. Can you give an example on how to get a TrialHandler2 object for the current trial?

Hope it works online soon :crossed_fingers:

6

Here’s my code, but it doesn’t have much more than was in my post: