Social psychology is best defined as the scientific study of

social influence

Explanation:

Social Psychology is defined as the scientific study of the way in which people's thoughts feelings, and behaviors are influenced by the real or imagined presence of other people.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.