What is a key observation method when conducting a Standardized Field Sobriety Test (SFST)?

The method of Horizontal Gaze Nystagmus (HGN) observation is a key component of conducting a Standardized Field Sobriety Test (SFST). HGN measures involuntary eye movements which can indicate varying levels of impairment due to alcohol consumption.

During the HGN test, an officer observes the subject's eyes as they follow a stimulus, typically a pen or a finger. The presence of distinct nystagmus (jerking of the eyes) when the eyes follow the stimulus can suggest that the individual has a Blood Alcohol Concentration (BAC) above the legal limit. This method is supported by extensive research and is considered reliable for indicating potential intoxication.

This technique is distinct from the other options, as finger dexterity evaluations and vehicle inspections do not directly measure impairment related to driving abilities, and listening to verbal responses, while providing some context, does not offer a standardized measure of physical indicators of impairment. Thus, the HGN observation serves as a critical scientific method within the SFST framework, backed by training and protocols established for law enforcement.