What is the main psychological principle behind the SFST?

The main psychological principle behind the Standardized Field Sobriety Test (SFST) is that impairment affects both physical and cognitive abilities. When an individual is under the influence of alcohol or drugs, their ability to perform tasks that require coordination, balance, and attention is significantly diminished. This impairment manifests not just in their physical ability to navigate tasks, but also in cognitive functions such as judgment, reasoning, and information processing.

The SFST is designed to evaluate these aspects by assessing how well a person can follow instructions, maintain balance, and perform tasks that require a combination of motor skills and cognitive processing. This comprehensive approach ensures that law enforcement officers can more accurately determine a driver’s level of impairment instead of focusing solely on physical performance or decision-making speed alone.

By recognizing that both cognitive and physical capacities are affected by impairment, the SFST provides a holistic view of a person's overall functioning while under the influence, which is crucial for assessing driving capability and ensuring road safety.