Final answer:
Hermann von Helmholtz contributed to psychology by measuring the speed of neuronal conduction, which was significant in understanding the physiology behind sensory experiences.
Step-by-step explanation:
Hermann von Helmholtz made an important contribution to psychology when he Measured the speed of neuronal conduction. Helmholtz was a German scientist who conducted research on the speed at which nerve impulses travel through the body. His work laid the foundation for our understanding of the nervous system and the transmission of information in the brain.
An important contribution that Hermann von Helmholtz made to psychology was when he c) Measured the speed of neuronal conduction. Helmholtz was a German physicist and physician who made significant contributions across different fields, including psychology, where he applied his expertise in physics to understand physiological processes behind sensory experiences. He was not directly involved with conditioned reflexes, cognitive dissonance, or moral development stages—those areas were developed by other scientists like Ivan Pavlov, Leon Festinger, and Lawrence Kohlberg, respectively.