Uncovering the visual features relevant to human visual scene processing Restricted; Files & ToC

Cheng, Ruu Harn (Summer 2022)

Permanent URL: https://etd.library.emory.edu/concern/etds/fx719n824?locale=en


Decades of neuroimaging studies have revealed a dedicated cortical network that is selectively involved in human visual places (or “scenes”) processing, including the parahippocampal place area (PPA) (Epstein & Kanwisher, 1998), the retrosplenial complex (RSC) (Maguire, 2001) and the occipital place area (OPA) (Dilks et al., 2013). But what exactly characterizes visual inputs as a “scene” (versus an object, for example) and thereby selectively engages the cortical scene processing system? Here, I propose that visual scenes can be characterized by a set of visual features that are common and unique to visual scenes, and identify two of such features. In Paper 1, I hypothesized that since we are always inside a scene, and interact with the outside of an object, concavity is a diagnostic feature of visual scenes. Consistent with my hypothesis, I found that two scene-selective cortical regions—PPA and OPA—responded selectively to visual cues of concavity, in scene and even object stimuli; moreover, participants also behaviorally judged concave over convex scene and object stimuli to be more like a scene. In Paper 2, using a stimuli-driven approach, I uncovered another visual feature common and unique to visual scenes—vertical luminance gradient (VLG)—and hypothesized that VLG is another diagnostic feature of visual scenes. Consistent with my hypothesis, I found converging neural and behavioral evidence for VLG as a visual feature that humans use for visual scene recognition. In Paper 3, I next asked: Having recognized visual inputs as a “scene”, how then do humans discriminate between different scenes (e.g., a kitchen versus a beach)? Building upon evidence in the existing literature, I hypothesized that color is a visual feature that humans use for visual scene discrimination, and tested whether color is used for visual scene discrimination more specifically, or discrimination of all kinds of visual stimuli more generally (e.g., objects too). I found that participants selectively used color for behavioral visual scene over object discrimination. Moreover, using an existing fMRI database, I also found that color better explained the pattern of response in PPA than an object-selective region (the lateral occipital complex; LOC). Taken together, these findings shed light on the unique properties of visual scenes, and provide insight into how and why visual scenes engage distinct cortical processing in the human visual cortex.

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