Is heart rate a better mousetrap for capturing emotional status in infancy? Campos' chapter convinces me, with an impressive array of evidence, that it can serve as an index for orienting and arousal, perhaps a more sensitive one than behavioral observation. His logic is that (1) behavioral evidence of affective arousal correlates with heart rate (HR) changes; (2) HR changes are more sensitive to emotional states than behavioral measures are; therefore (3) HR may be a better measure of subtle developmental shifts and changes in state than other psychophysiological and behavioral measures.
He is careful to note, however, the shortcomings of the HR measure: It responds to internal and external stimuli other than emotional state; it does not give information about the specific emotion aroused; and it tells us nothing about the psychological processes that accompany orienting or arousal. In short, HR is a measure at the physiological, not the psychological, level.
Emotional states during infancy--and at all other ages--involve responses at both psychological and physiological levels. As psychologists, we are presumably more interested in the cognitive and behavioral aspects of emotional development than in the physiological ones per se. To the extent that HR provides information about the psychological meaning of emotional states, it is a useful tool in the study of emotional development. If HR only provides information about the physiological level of response in emotionally arousing conditions, then I contend that we should be no more interested in HR than in, say, the digestive process. Understanding obesity may involve understanding digestion, but digestion is unlikely to