Object, face, body and scene representations in the human brain

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The goal of this research is to understand how we see what we see: how does the brain analyze the light falling on the retina of the eye to reveal a world full of objects, people and things? During the past year we have focused on both (i) perception and (ii) memory of complex visual stimuli, in particular real-world visual scenes, objects and people (NCT00001360). Perception: Real-world scenes are incredibly complex and heterogeneous, yet we are able to categorize them and identify objects and people within those scenes effortlessly. While prior studies have identified brain regions that appear to be specialized for processing faces, object and scenes, it remains unclear what the precise roles of these different regions are and what information they contain. One of the major challenges in understanding visual perception in the brain is the wide range of different objects and scenes that we experience. Despite this breadth, studies often focus on a small number of hand selected object or scene categories, but it becomes unclear how representative any subsequent findings are. To overcome this challenge we developed a large-scale database (THINGS) of 1,854 diverse types of object sampled systematically from concrete picturable and nameable nouns in the American English language. This database provides a rich resource of object concepts and object images and offers a tool for both systematic and large-scale naturalistic research in the fields of psychology, neuroscience, and computer science. We used this database in a large-scale behavioral experiment using online crowdsourcing, sampling 1.46 million trials in more than 5,000 participants. Using a computational model of the task, we were able to identify 49 core dimensions of our internal mental representations of objects, providing a comprehensive and fine-grained characterization of this representational space. These results provide important insights into the cognitive processes supporting our understanding of objects. We are now extending this work to reveal the underlying brain mechanisms by collecting fMRI and magnetoencephalography (MEG) data for this diverse set of object images. Memory: To understand the nature of object and scene memory, we have focused on two specific issues: 1) Organization of the medial parietal cortex Human medial parietal cortex (MPC) has been implicated in multiple cognitive processes including memory recall, visual scene processing and navigation. Given such diverse recruitment of MPC across cognitive domains historically considered largely independent, it is not surprising that there has been no clear consensus with regard to its function and overarching organization. In a series of studies, we measured brain activations with fMRI while we presented participants with images of scenes and people and also asked them to recall specific events (e.g. shaving, going to a beach) as well as recall famous or personally familiar places and people. Our findings revealed two key insights. First, we found an apparent gradient of representation from more perceptually related to more memory related from posterior to anterior within MPC. Second, we found distinct subdivisions within MPC that were active differentially during recall of either people or places. While people and places are two of the most important things we recall from memory, we can also recall specific objects, and separate regions have been identified in visual cortex that appear to be specialized for processing faces, scenes and objects. In follow-up studies we have been addressing whether recall of objects also recruits a separate region in MPC, and how the activations elicited by recall of objects and scenes compares with that elicited by perception of the very same stimuli. Collectively, these results provide a new framework for understanding the functional role of MPC and its significance during different aspects of cognition. 2) Elucidating the content of scene memory When we recall a previously experienced event, what exactly are we remembering? Are our memories a precise, high-definition recording of that event, a low-resolution gist of that memory, or even just a verbal description of what we saw? Answering this question is an essential component of being able to tease apart the mechanisms of memory: what information is encoded and maintained, how memory decays over time, and what information is retrieved from these memories. In a series of studies, we have been investigating the content of memory for real world scenes using a drawing task. Participants study scenes and then after a delay, draw those scenes in as much detail as possible from memory. The resulting memory-based drawings are scored by thousands of online observers, revealing numerous objects, few memory intrusions, and precise spatial information. We have studied both young volunteers as well as people who claim to have no visual imagery (termed aphantasia). Further, we have investigated a common distortion that occurs in memory in which the boundary of the scene is either extended or contracted. Our findings show that not only is it possible to quantify the content of memory during free recall, but that those memories contain detailed representations of our visual experiences (although memory distortions may still occur). Elucidating how the brain enables us to recognize objects, scenes, faces and bodies provides important insights into the nature of our internal representations of the world around us. Understanding these representations is vital in trying to determine the underlying deficits in many mental health and neurological disorders.