Final answer:
In the faces experiment, normal persons may perceive the face with the happy half on the left as happier, due to the left hemisphere's specialization in processing positive emotions. Persons with left side neglect might perceive the face with the happy half on the right as happier because they might not fully process stimuli on the left.
Step-by-step explanation:
In the faces experiment, when presented with a face that has a happy expression on one half (either left or right), a normal person tends to perceive the half with the happy expression as being more expressive of happiness. The leading perception of happiness would likely depend on which side of the face carries the happy expression. Given the research findings that point to the left hemisphere of the brain being more involved in processing positive emotions, a normal person might be inclined to perceive the face with the happy half on the left as happier overall due to this hemispheric specialization in processing emotional expressions.
However, a person with left side neglect, a condition often resulting from a right hemisphere brain injury, may ignore or be less aware of stimuli on their left side. Therefore, they may perceive the face with the happy half on the right as happier because they may not fully process or attend to the left side of the face. It's worth noting that the brain operates as a whole, and while certain functions may have hemispheric dominance, both hemispheres interact to produce behaviors and perceptions.