When we are afraid the heart races, breathing becomes rapid, the mouth dries up, muscles tense, and palms become sweaty. We may feel anxious, stressed, panicked or nervous, but emotion recognition does not end here. Psychophysiology shows us that such changes are mediated by the autonomic nervous system (ANS), which operates the sympathetic and parasympathetic divisions of the human body.
The sympathetic nervous system (SNS) is a “quick response mobilizing system” responsible for “fight or flight” responses, which prepare the body to react to stresses such as threat or injury. It directs muscles to contract and heart rate to increase. The parasympathetic nervous system (PNS) is a “more slowly activated dampening system” referred to as “rest and digest”, which controls functions of the body at rest. It helps maintain homeostasis by directing muscles to relax and heart rate to decrease. In conjunction, the two constitute what psychophysiologists refer to as the ANS.
Although both the sympathetic and parasympathetic divisions drive opposing effects on the body, it is the balance of activity between the two that helps maintain an internal stable environment in the face of changing external stimuli and conditions. During an anxious experience for instance, the body will divert blood flow from parasympathetic nerve functions (such as digestion) to sympathetic nerve functions (such as muscle contraction and heavy breathing).
There is little people can do to consciously control their PNS, but there are factors (such as exercise and experience) that can help some people exert a level of control over the sympathetic responses. Certain emotional states affect this balance and can result in a wide variety of bodily reactions similar to the ones described in brackets above. Importantly, these bodily reactions can be monitored and measured through signals referred to as bio-signals.
All we can observe from the outside are the bodily reactions. Bio-sensors give us insights into how and why these reactions are occurring across the interplay between parasympathetic and sympathetic nerve functions. As a result, detection and analysis of the these involuntary, subconscious divisions of the body are becoming an increasingly important field for Human Computer Interaction (HCI) as the advantages of emotional recognition and machine learning become more apparent and achievable online and across everyday life.
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