Sikun Lin successfully defends her Phd on the topic of "Representation Learning on Brain Data".

Committee: Ambuj Singh (Chair), Tommy Sprague, Xifeng Yan

Artificial intelligence and machine learning (AI/ML) have been extremely successful in predicting, optimizing, and controlling the behavior of complex interacting systems. Robustness and explainability of existing AI/ML methods, however, remain big challenges, and clearly new approaches are needed. The human brain motivated the early development of deep learning, and neuroscientific concepts have contributed to the profound success of deep learning algorithms across many areas. The next leap in AI/ML may again come from a deeper understanding of brain architectures and processes---this dissertation focuses on deepening this understanding with machine learning models. This talk will briefly present (1) a convex optimization framework to analyze and integrate multimodal brain data to infer brain subnetworks and understand heterogeneity across tasks, (2) a novel deep learning to learn representations of multimodal and dynamic brain signals. Although these models are mostly considered black-box, we can characterize the input brain signals with attribution methods, study brain organizational structures, and unveil the heterogeneity among brain regions, tasks, and individuals. Next, as the main focus of the talk, I will discuss (3) how semantic representation is an essential piece of the human visual system. With added text modality, we are able to reconstruct complex high-fidelity imagery from input brain signals and infer brain activities from visual stimuli. Further studies will also be presented to explore (4) the redundancy and dependency in these brain signals related to visual information processing. Lastly, I will briefly discuss two works in which (5) we applied neuroscience tools and insights to deep learning models, gaining a deeper understanding of the latter and developing more computation- and memory-efficient models. These works demonstrate that advances and challenges in neuroscience and AI/ML benefit each other and drive both fields forward.