At about what age does infants' smiling indicate feelings of happiness?

What do many researchers use as an operational definition of anxiety?

a. An increase in the pupillary reflex b. A decrease in the grasp reflex c. An increase in the startle reflex d. A decrease in the knee-jerk reflex

According to the textbook, the key distinction between philosophy and psychology is the fact that psychology ____

a. is concerned with observable phenomena (e.g., behaviors) rather than unobservable phenomena (e.g., thoughts) b. is concerned with unobservable phenomena (e.g., thoughts) rather than observable phenomena (e.g., behaviors) c. primarily relies on the scientific method d. primarily relies on the case study method