Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

The autonomic nervous system (ANS) controls the activity of the body's internal organs and regulates changes in their activity depending on the current environment. The vagus nerve, which innervates many of the internal organs, is an important part of the system. When our brain senses danger, vagal tone is inhibited, leading to a set of changes in the body designed to make us more prepared to fight or flee; for example, our heart rate increases, our pupils dilate, and we breath more quickly. Conversely, when the vagal system is activated, these physiological responses are inhibited, leading to a calmer state. The vagus nerve, then, acts as a kind of "brake" on our arousal. One interesting consequence of this calmer state is that it tends to promote social interaction-when we are not tensed and afraid of our immediate environment we are instead receptive to interacting with others. Poor functioning of this regulatory mechanism, therefore, may be associated with difficulties in social behavior.

One index of autonomic regulation is heart rate variability (HRV). HRV is a measure of how much the gap between one beat and the next varies over time. High HRV means there are continual fluctuations in the heart rate over time, a reflection of successful autonomic regulation. Low HRV means there is consistency of the heart rate over time, a condition associated with poor autonomic regulation.

In this study we will test the hypothesis that increased HRV is associated with more accurate categorization of emotional stimuli.^1,2 Following a study by Park et al., we will measure HRV and test its association on a task that measures skill at perceiving facial emotions.³

1. Recruit 40 participants.

1. Participants should have normal or corrected-to-normal vision to ensure they will be able to see the stimuli properly.
2. Participants should not consume alcohol, caffeine, or other drugs for at least 6 hrs prior to the experiment.
3. Participants should have no history of neurological, psychiatric, or cardiac disorders.

2. Pre-experiment procedures

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