A research project conducted with three-year-olds in a Los Angeles preschool tested children's spatial reasoning after eight months of keyboard and singing lessons. The children who had received the music training increased their spatial-temporal reasoning by 46 percent as compared to a 6 percent increase in the control group that received no training.
Frances Rauscher, Gordon Shaw, Linda Levine, Eric Wright, Wendy Dennis, and Robert Newcomb, "Music Training Causes Long-term Enhancement of Preschool Children's Spatial-Temporal Reasoning." Neurological Research, vol. 19, February 1997.

Researchers studying the link between music and intelligence divided preschool children into four groups: one group received private piano lessons, the second had private computer training, while the remaining children were divided among a singing-only group and a no-lesson group. After six months of training, the groups were tested. Those in piano group had the most dramatic improvement in spatial-temporal reasoning: their scores increased by 34 percent.
Amy Graziano, Gordon Shaw, and Eric Wright. "Music Training Enhances Spatial-Temporal Reasoning in Young Children: Towards Educational Experiments." Early Childhood Connections, Summer 1997.

Irvine's Center for Neurobiology of Learning and Memory found that preschoolers who had received eight months of music lessons scored 80 percent higher on object-assembly tasks than did other youngsters who received no musical training. That means the music students had elevated spatial temporal reasoning -- the ability to think abstractly and to visualize physical forms and their possible variations, the higher-level cognition critical to mathematics and engineering.
The Power of Music, Laura Elliott, The Washingtonian, December 1995

Music Instruction enhances spatial-temporal reasoning for preschool and elementary age children while instruction is occurring, and through at least two years of such instruction
Lois Hetlan, Journal of Aesthetic Education, Fall/Winter 2000

Students with musical training apparently have a greater capability to process all sounds, including speech.
 Music Training and Mental Imagery Ability. By A. Aleman, M.R. Nieuwenstein, K.B. e. Bocker, and E.H.F. de Haan. Published in Neuropsychologica, Vol. 38 (2000), pp. 1664-1668