SAT Inferences Question

Many believe that lullabies, characterized by their slow tempos, contain some acoustic features that are universally calming to infants. In a study, Constance M. Bainbridge and colleagues played both a lullaby sung in the Luk Saami language and a non-lullaby sung in the Tundra Nenets language to a group of infants. The researchers also measured the infants' heart rates, as a reduced heart rate is considered a measure of relaxation. They claim that the lullaby did indeed relax the infants. Which finding, if true, would most directly support Bainbridge and colleagues' claim?