Answer:
b. interaction effect
Explanation:
Based on the information provided within the question these differences are called an Interaction Effect. Like mentioned in the question this effect refers to the effect that two or more independent variables have when combined together on a specific dependent variable which either increases or decreases significantly the effect as opposed to being separate. Which is what the researcher is trying to detect by combining different independent variables such as fast music/bright lighting or fast music/dim lighting, etc.
I hope this answered your question. If you have any more questions feel free to ask away at Brainly.