What does the modern polygraph primarily assess?

The modern polygraph primarily assesses changes in the physical autonomic nervous system. This includes monitoring physiological responses such as heart rate, blood pressure, respiration, and skin conductivity while a subject answers questions. These physiological responses can indicate stress or emotional reactions that may correlate with truthfulness or deception during the questioning process.

The polygraph operates under the premise that deceptive answers may trigger a physiological response due to the individual's anxiety or fear of being caught in a lie. Therefore, the primary focus of the polygraph is on these physical changes that are reflective of the workings of the autonomic nervous system, which operates involuntarily and is sensitive to emotional states.

Other options, while they may relate to aspects of crime investigation or interrogation processes, do not accurately capture the primary function of the polygraph. For instance, assessing confession validity or witness reliability involves subjective analysis of statements and credibility rather than measuring physiological responses. Likewise, maintaining crime scene integrity includes securing evidence and ensuring that the scene is undisturbed, which lies outside the scope of what the polygraph is designed to evaluate. Thus, the polygraph’s focus is distinctly on physiological changes, confirming that option relating to the autonomic nervous system is the most accurate representation of its primary assessment focus.