More interestingly, from ScienceNOW (link added):
As expected, these subjects did not have the typical MMN response to poorly played tunes, the team reports today in PLoS One. But to their surprise, the researchers did detect the P300 response to the incorrect notes. Braun believes these results show that the brain can detect the differences even though tune-deaf people aren't aware.
Thus these subjects possibly have a deficiency in transfer between conscience and unconscience knowledge of incorrect tones. The authors of the paper propose:
In light of this, TD may provide a novel opportunity to study conscious perception. Unlike lesion-based disorders such as blindsight it should be possible to study the process in a brain that is structurally intact, and in a patient population that is far larger. In addition, TD is a highly heritable condition, and investigations currently underway may identify the genetic variants that underlie this condition. The tune deaf population may thus constitute a group in which the problem of consciousness might be approached at the cellular and molecular level using the tools of genetic research.