When studying infant state regulation in response to pain, researchers may present different

substances, such as water or sugar (sucrose) and administer these substances via either a
pacifier or a dropper.

Why are these manipulations necessary?  What are some common
findings from studies that use these methods?
What will be an ideal response?

The researcher is essentially manipulating 2 variables in such a study. One would be
substance, water or sugar, and the other would be level of tactile stimulation. That is,
the infants may derive pleasure from sucking on a pacifier, but will not obtain tactile
sensation from a dropper. Thus, one could envision 4 experimental conditions
(water-pacifier; water-dropper; sucrose-pacifier; sucrose-dropper). In such studies,
researchers have noted that infants that are supplied sucrose are more likely to quickly
calm down and stay regulated after a painful procedure. This finding would suggest
that sucrose has important effects on state regulation and these effects are not due to
tactile stimulation—it does not seem to matter whether the substance is delivered via
pacifier or dropper.