Our selection committee generally viewed participation in research as an indicator of drive and leadership potential. That being said, we really only paid attention to excellence. If you spent a summer extracting juice from rat pineal glands that resulted in 7th authorship on a conference abstract, that would elicit a yawn. If you spent most of your medical school career working with the same faculty member, demonstrated a deep interest in understanding racial disparities in access to HIV antiretroviral therapy and netted some 1st/3rd/7th author publications -- then, even though the research was not psych-related, it would be perceived as a noisy measure of some degree of promise that might in the future be applied to psych (eg., whether as a leader in organized psychiatry, as a leader in a clinical setting, or as a leader in psych research, etc).
If you were a marginal candidate (i.e., via grades, letters, personal statement, etc) then having "research experience" -- whether it consisted of one summer's worth of pipetting or whether you had obtained multiple first-authored publications -- never really helped you. Similarly, for marginal candidates we tended to overlook letters of reference from research supervisors. Our priority focus was on attempting to discern whether an applicant would make a good psychiatrist and a good psychiatry resident. Bottom line, from the perspective of our specific selection committee, research couldn't help compensate for critical deficiencies in a marginal application.
