Merleau-Ponty's main interest, before he started to be a phenomenologist, were Henri Bergson's philosophy, Gestalt psychology, and neurology.
In his "Structure of Behavior", he denies the notion of reflex. Because it requires one-to-one correspondence between the stimulus and the response.His claim was that the Organisms response to the meanings of the environment or situation, not to the stimuli. Thus the behavior cannot be explained as a complex of reflex acts. He stresses the importance of behavior but it's totally different from that of behaviorist.