Answer:
the noise level during the encoding task
Step-by-step explanation:
An independent variable in the context of an experiment is the part of an experiment that is being tested and does not depend on some other part of the experiment. Which in this case would be the noise level during the encoding task. That is because the noise level is the variable that is being changed for each group and does not depend on anything else, unlike the memory test which depends on the noise level.