I’ve had recent graduate applications from students who have either started or in one case completed degrees in the arts, usually music, and then switched into physics. I am particularly interested in these students. There is nothing more important in a good and creative scientist than the ability to see things in ways others do not, and thus to discover new things others do not see. Each area of human experience brings with it its own perspective, a set of biases, values, and approaches to problem solving that is optimal for that field. The issue is that in discovery, it is (almost by definition) not clear what approaches work, so being able to approach problems from more than one perspective is very valuable.
This past year during graduate admissions, I perked up when not one but two good candidates appeared with music backgrounds. Each had started music school (one in piano, the other in voice) and had transferred to a university after a few years to pursue a degree in physics. While their grades in physics were only average, both were cited by their research supervisors as being particularly creative and self-motivated. Some of this is due to the student and not the former field of study: students who transfer tend to know what they want and be willing to go get it. However, it is my belief that a broad background that includes some actual training in areas far from the current field of study is excellent preparation for success in the sciences. Conversely, when I see applicants who have done nothing but study physics since fetushood, I worry.