Final answer:
The polygraph measures changes in physiological arousal that accompany emotion, based on theories like the James-Lange theory of emotion. However, the effectiveness of polygraphs is debated since physiological responses can be similar for different emotions and influenced by cognitive appraisal as proposed by Schachter and Singer.
Step-by-step explanation:
The polygraph measures the changes in physiological arousal that accompany emotion. This idea is supported by theories that suggest emotions arise from physiological changes in our body. For example, the James-Lange theory of emotion asserts that emotions are the result of these physiological changes. According to this theory, we first experience physiological arousal, such as an increased heart rate or sweating, and then we experience the emotion connected to that arousal. In the context of the polygraph, it measures various physiological reactions including heart rate, blood pressure, respiration rate, and skin conductivity in the belief that these will change when a person experiences the emotion associated with lying.
However, the actual effectiveness of the polygraph as a lie detector is questionable. This is in part because, as Schachter and Singer proposed, physiological arousal might be similar across different emotions, and it is the cognitive appraisal of the situation that dictates the specific emotion experienced. Therefore, it's difficult to attribute changes in physiological arousal to lying specifically, rather than to other emotions or emotional states. Physiological responses might be seen when a person is anxious or stressed, which could occur for many reasons other than deception.