Ge, Yijun2021-09-242021-09-242021-06https://hdl.handle.net/11299/224679University of Minnesota Ph.D. dissertation. June 2021. Major: Psychology. Advisors: Sheng He, Daniel Kersten. 1 computer file (PDF); v, 96 pages.Our visual system samples external information, adjusts its sensitivity and constructs a stable representation of the world that allows us to perceive and interact with objects in our environments. Visual information with different levels of complexity is processed through the hierarchically organized visual cortical areas. This dissertation presents three studies exploring the neural processing of visual stimuli at different cortical levels associated with feedforward and feedback processes. Study 1 investigates whether cortical neurons adjust their sensitivity based on stimulus-driven feedforward or perception-related feedback signals when they are discrepant, using psychophysical and neuroimaging techniques. We found that feedback signals associated with perception dominantly contribute to neural sensitivity control. Study 2 explores the properties of viewpoint-independent spatiotopic reference frame transformation for simple and complex visual stimuli using a trans-saccade adaptation paradigm. The results showed that both simple (orientation) and complex (face gender) visual features could be transformed into the viewpoint-independent spatiotopic reference frame, even in the absence of visual awareness of the target objects. Study 3 examines the viewpoint-dependent and viewpoint-independent neural representation of a complex stimulus feature (human pose information in natural images) in distinct dimensions (2D vs. 3D) using representational similarity analysis of 7T-fMRI data. The results revealed a distributed neural representation encoding different aspects of human pose features, with the 3D viewpoint-independent pose information captured at the posterior superior temporal sulcus, and body viewpoint information mainly encoded near the extrastriate visual cortex. Together, these studies help us to understand the importance of feedback signals in cortical sensitivity control, the awareness-independent transformation of visual objects from retinotopic to spatiotopic reference frame, and the distributed representation of body pose features in the visual cortical hierarchy.enThesis or Dissertation