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Black boxes replace stimuli after several trials


I am running an experiment online through Pavlovia. For some people (it seems Mac users in particular), part way through the experiment the stimuli become replaced with black boxes and it continues to present black boxes until an ‘unspecified java script error’ appears.

Has anyone experienced this issues/knows how to resolve it?

Thank you!

That sounds like a memory issue. Are you updating anything every frame?

Can you use the console to obtain a more specific error message?

Please take a look at my crib sheet (pinned post).

Best wishes,


Hi Wakefield,

Thank you for such a quick response.

The stimuli are set every repeat in builder as they change on every trial. I can see it says not to do that on your crib sheet. Is there an alternative way to do this? (This is the first experiment I have made in PsychoPy so am not very familiar).

Thank you!

Every repeat should be fine – it’s just every frame that causes an issue.

I just checked through the experiment and it is always set to every repeat when something is changed. I have a fair bit of in line code in some routines but variables are defined at the beginning of the experiment and code is written in 'begin routine" rather than “each frame”.

Unfortunately, I am not able to replicate the problem myself to get more specific error message. It does seem to only happen if using Safari.

What file type are the stimuli?

I have a visual cue which is a jpg with a word displayed on top in a white box. The word and picture change on every trial.

Both the picture and word are linked to a variable using $ which is defined in an excel file for the loop

I’ve now got this on my own experiment. The researcher tried it with an iPad and got black rectangles instead of text from trial 63 of 200. I have a mouse location check every frame for the touchscreen response but updates are each routine. I’ll try replacing the Each Routine update with .text= in the Begin Routine code and see if that helps.