Answer: The correct answer for the blank is-
B. sociocultural.
Sociocultural theory for learning was proposed by psychologist Lev Vygotsky. According to this, behavior of an individual can be influenced by his surrounding that includes caretakers, society, peers, and culture at large.
As per the information in this question, a team of psychologists is studying how negative feedback ( a reaction that leads to decrease in the function/ activity) affects self-esteem in different cultures.
Therefore, it indicates that the psychologists are working from the sociocultural perspective.