I think that would depend in part upon the type of psych research and what you're hoping to do w/ your MD (and therefore express in your PS). History research is always non-clinical and doesn't really have many similarities to basic research either, so that'd be a bad choice; however, there is clinical research in psych (just like in medicine) and many psychologists study areas closely related to medicine (clinical, neuro, clinical neuro, health/preventative, etc.). If you did research in an area closely related to medicine, it should be viewed positively.
Also, it's noteworthy that psych research uses many of the same research methods as does biomedical; as a result, the experience would be valuable. On the other hand, history research is going to be largely archival, which is going to require a very different set of tools.