Final answer:
Healthy controls may prefer faces smiling on the left side due to the left hemisphere's dominance in processing positive emotions and language functions. This hemisphere controls the right side of the body, leading to a potential preference for smiles on the right side of a person's face, which appears on the left visual field.
Step-by-step explanation:
The preference for faces smiling on the left side among healthy controls could be influenced by lateralization in the brain's hemispheres, which implies that there is a specialization of function in each. As researchers like Gazzaniga have suggested, the left hemisphere is often dominant for language functions and positive emotions, while the right hemisphere is associated with negative emotions. Since the left hemisphere controls the right side of the body, and hence, the right side of the face, this dominance could potentially result in a preference for stimuli like smiles on the left visual field (right side of the face).
The facial feedback hypothesis also plays a role, indicating that facial expressions can affect emotional experiences. If healthy individuals tend to experience more positive emotions when viewing smiles, which are expressions commonly associated with positivity, then they may inherently prefer faces that smile on the side of the face controlled by the dominant hemisphere (left hemisphere, right face side).