One effective approach is to manipulate different conditions of your task in a pilot study and then use a psychometric function to examine how performance varies across conditions. This allows you to estimate the difficulty level of your task under each condition, which is a common method in psychophysical research.

I recommend using the Palamedes Toolbox, which provides tools to fit and analyze psychometric functions: 🔗 https://www.palamedestoolbox.org/

I also suggest the book "Psychophysics: A Practical Introduction", which offers a clear explanation of psychophysical methods and how to apply Palamedes in practice.