Linda Ann’s Answer
graduate school admissions to PhD programs is highly competitive. (I operate under the assumption that a terminal degree is indeed your goal). Thus, research experience in a laboratory of one of the psychology faculty members is really important for your c.v. IF you Can find a suitable internship or two which supports the psychology specialty in which you are interested in a doctoral level program, that too will bolster your chances of admission to grad school.
If you have a keen interest in the biological basis of behavior, then persue the double major. I strongly recommend conversations with your psychology faculty advisor on such matters.
Because the competition for admission has become so keen in the past decade, your scores on the Graduate Record Examination (GRE) must be quite high. Many students are thus perusing a master's degree, focusing on developing their research skills as a stepping stone into PhD programs.
So, Perdue research/internship experiences. Work diligently with whomever is mentoring you...so that they will be in a position to write you strong letters of recommendation to grad school.