When people or cockroaches undertake a difficult task, the presence of others performance; whereas when they undertake a simple task, the presence of others performance.

impair;enhance.

Explanation:

the blank will be filled with impair;enhance.

When undertaking difficult task the presence of others degrade or weakens  the performance of the people.

And when undertaking the simple task the presence of other enhance the  performance of the group.

This is because difficult work require more concentration and presence of other person affect the efficiency of the person.

imagine me knowing the answer

answer; participant observation method;