Listening to loud music has a small effect on reaction time. Music at low and moderate levels does not affect reaction time in a significant way.
The Mozart Effect concluded in 1999 that listening to classical music temporarily improved spatial reasoning. Since then, studies have been done to determine the effects of different kinds of music on a variety of kinds of tasks, including reaction time. The spatial reasoning improvements originally seen were done using a Mozart recording, but other studies broadened to include other composers and types of music. The effect on spatial reasoning lasts 10 to 15 minutes after listening to the music. There have been varied results to these studies, and some question whether the Mozart Effect exists at all.
A study done by Edward Mjoen of Winona State University, concluded that music does not have a significant effect on reaction time. A study done in Jan. 2000, by Susan Strick focused on different volumes of music and how they affected the reaction time of drivers. Ten teenage females were tested on driving skills while listening to music. Their reaction times were slowest when the music was the loudest, at 95 decibels. The difference, 0.12 seconds, does not sound significant but means the difference between a near miss and a crash. Listening to music does not improve reaction time, and loud music hinders it.