Which two measures are most frequently used to reflect an infant's awareness of a change in an event?

The choice that highlights the most frequently used measures to reflect an infant's awareness of a change in an event is the combination of facial expression and vocalization. Infants communicate their awareness and reactions to their surroundings through these two expressive forms.

Facial expressions can convey a wide array of emotions and responses, such as surprise, curiosity, or discomfort, allowing caregivers to gain insights into how the infant is processing changes in events or environments. For instance, an infant might widen their eyes in surprise at a sudden sound or frown when confronted with something unfamiliar.

Vocalization also plays a crucial role. Infants use sounds ranging from cooing to crying to signal their feelings and reactions. Changes in these sounds can indicate various states of awareness or emotional responses to new stimuli.

In contrast, while other measures such as heart rate and level of activity are important observable behaviors, they may not directly communicate an infant's subjective experience or awareness of changes. Similarly, eye movement and sucking reflexes provide insights into sensory engagement and needs but do not specifically reflect awareness of changes in events as clearly as facial expressions and vocalizations do.