Over the past year, the Physics and Astronomy Department at San Francisco State University (SFSU) has implemented a pedagogical training course for incoming graduate teaching assistants (GTAs). While it has been widely accepted that students' sense of belonging in the classroom can be influenced by many factors, our focus is to better understand what students themselves feel contributes most to their sense of belonging and what role GTAs might play in it. We have collected attitudinal surveys from students in the introductory physics sequence for life science majors that pertain to students' perceptions of belonging and relationship to their lab instructor. We have identified an emergent set of factors from student testimonies, showing a number of indirect influences GTAs may have on students' sense of belonging in lab. We found students tend to cite interpersonal relationships with their group and the labwork itself as major contributors to their sense of belonging in Physics I while Physics II students prioritize interpersonal relationships with both their group and the class as a whole. Our goal is to develop a set of student-centered approaches from this data that will ultimately provide insight for future lab instructors to help create an inclusive and accessible laboratory environment.