What confound refers to the tendency of study participants to, consciously or subconsciously, act in the way they think the experimenter wants them to act?

It is called "demand characteristic".

In experiments, especially in the subject of psychology, demand characteristics alludes to an experimental artifact where members shape an elucidation of the test's motivation and consciously or subconsciously change their conduct to fit that understanding. This influences information since members begin considering causal, gullible connections, and they endeavor to make sense of it this influences study's end data.