Generally, they’ve found that these patterns of brain activity tend to be weaker in people with ADHD, at least for some types of tasks. On top of that, it appears that ADHDers struggle with error processing in at least two different ways: first, with recognizing that they’re making an error in the early stages of doing so, and second, with reacting to that error and learning from it once it becomes clear a mistake has been made.
One reason researchers believe impaired error processing might be an important feature of ADHD is that error processing relates to more general aspects of ADHD like inattention. Think of it this way: someone who’s less attentive is also going to be less attentive to errors, and someone who doesn’t pick up on their own mistakes is probably paying less attention in general. In many situations, inattention and impaired error processing are two sides of the same symptom.
Differences in how people with ADHD react to errors also seem to relate to another key feature of ADHD: differences in how people with ADHD react to rewards. Overall, motivating people with rewards makes them better at recognizing errors. This is even more true for people with ADHD.
So, a general pattern that’s present for many ADHD symptoms holds for error processing deficits as well: differences in how people with and without ADHD process reward apparently play a role in other types of cognitive differences, and adding rewards can help normalize some of those other cognitive differences.