Alcohol usually: Question Alcohol usually: Answers Improves reaction time. Impairs depth perception. Improves night vision. Explanation Alcohol impairs a number of basic functions necessary for safe driving, including muscle coordination, reaction time, depth perception, and night vision. Operating a motor vehicle while under the influence of alcohol is both illegal and dangerous. This questions appears in the following tests: Maryland Class B Knowledge Test Mississippi Class A Knowledge Test New Mexico Class A Knowledge Test