Final answer:
Caleb, at four months old, will grasp a rattle using the reflexive, whole-hand grasp known as the grasping reflex, which is present from birth until around five to six months of age.
Step-by-step explanation:
Caleb, being four months old, will exhibit developmental capabilities typical for his age, which includes certain reflexes. One of these is the grasping reflex, which is an instinctive behavior wherein an infant will close their hand and "grasp" when an object is placed in their palm. This reflex is present from birth until around five to six months of age. Therefore, if Caleb grasps a rattle, he will do so using this reflexive, whole-hand grasp.
The grasping reflex plays an important role in maintaining close physical contact with the caregiver and satisfies the infant's basic need for physical interaction. At Caleb's age, the grasp reflex is complemented by other emerging voluntary movements, such as being able to roll from the front to side, lifting his head, and starting to make vowel sounds. However, the precision required for a pincer grasp, which involves using the tips of the thumb and forefinger, typically develops later, at around ten months old.