A few weeks ago, I described a study about how post-COVID, 15-20% of people had difficultly drawing a ‘stick figure’, known as the Rey-Osterrieth Complex Figure (ROCF), and I observed:

I have no idea what the implications of this are, for let’s say, surgery. Or driving. Or standardized test scores. Though I imagine good is the wrong adjective. \It’s also not clear if this is permanent–and they may learn to compensate by ‘remembering’ the image. But this is really… not good. And around twenty percent (remember, some will fail in the absence of COVID) is so high, that even if things like vaccination lower the chance of this happening, we’re still looking at a non-trivial fraction of people with this dysfunction several months after infection.

A recent preprint analyzed the results of 84,285 Great British Intelligence Test participants who completed a questionnaire about COVID-19 infection (suspected and confirmed). Even those who had mild symptoms not requiring hospitalization showed a decrease of 0.04 standard deviations in overall scores (“global cognitive scores”). When examined further, the subgroup of tests that examine semantic problem solving and visual selective attention were affected the most. In the study I discussed previously, the effects were largely seen on the ROCF, which assesses assess visuospatial abilities, executive functions, and memory, so the same broad classes appear to be affected.

In this study, unfortunately, the results are phrased exclusively as changes in standard deviations, which will mask how the changes happened: is this an across-the-board decline, or is an increased, but small percentage of test takers performing horribly. Hopefully, if they publish this study, the authors will report how many people who had COVID perform poorly (e.g., 1.5 standard deviations below the mean; this cutoff is the bottom 6.5% of pre-COVID test takers). We also don’t know what effect, if any, vaccination has (that wasn’t asked).

Still, if you are still trying to avoid (re)infection, you are not the weirdo. Because the flu–or a common cold–does not affect cognition like this in this many people.