Which of the following groups includes individuals who have made significant contributions to the understanding of psychology?

The group that includes individuals who have made significant contributions to the understanding of psychology is indeed the one featuring Edward Hall, E.L. Thorndike, and B.F. Skinner. Edward Hall is known for his work in cultural anthropology and the concept of proxemics, which studies how space is used in social settings and its psychological implications. E.L. Thorndike is recognized for his research in educational psychology, particularly his work on the laws of learning and the development of the first intelligence tests, which laid groundwork for modern testing. B.F. Skinner was a prominent behaviorist who conducted research on operant conditioning, significantly influencing the field of psychology with his studies on behavior and reinforcement.

The other groups consist of individuals whose contributions primarily lie outside of psychology. For instance, Herodotus and Thucydides were ancient historians who focused more on the fields of history and political analysis. Adam Smith, Milton Friedman, and John Kenneth Galbraith are all economists and their work, while influential in economic theory and policy, does not directly pertain to psychology. Similarly, Thomas Jefferson, Karl Marx, and Henry Kissinger made their marks in political philosophy, governance, and international relations, but do not directly contribute to the field of psychology