Geoffrey Hinton (Google Scientific Advisor) – How to represent part whole hierarchies in a neural network | ACM SIGKDD India Chapter (Jan 2021)
Chapters
00:00:50 Advances in Neural Network Research for Human-Like Vision Systems
Introduction: Geoffrey Hinton’s background in AI, neural networks, and deep learning. His significant contributions to speech recognition, object classification, and neural network research. His numerous prestigious awards and recognitions.
Keynote Talk Overview: Hinton discusses his current focus on combining recent advances in neural network research. Aim to create a new vision system similar to human perception. Acknowledges that the system is imaginary but believes it will work.
Part-Whole Hierarchy and Coordinate Frames in Human Perception: Hinton introduces his key concept of the part-whole hierarchy in human perception. Explains how humans perceive objects as a collection of parts and wholes. Introduces the idea of coordinate frames in human perception, which provide a reference for locating objects in space.
00:03:24 Understanding Structural Descriptions in Neural Networks
Introduction: Geoffrey Hinton discusses the concept of structural descriptions in mental images, demonstrating through a mental exercise that people perceive and understand objects differently using internal coordinate frames.
Demonstration with a Cube: Hinton asks the audience to imagine a wireframe cube resting on a tabletop and manipulate it mentally. Most people struggle to correctly identify the corners of the cube when they move the top corner vertically above the bottom corner.
The Zigzag Ring Structure: The actual structure of the cube is a zigzag ring of edges connecting the corners. This structure is often overlooked because it differs from the rectangular coordinate frame typically used for understanding objects.
Multiple Interpretations of the Same Arrangement: The same arrangement of rods can be perceived in different ways, leading to different understandings and awareness of the object’s properties.
Structural Descriptions: Hinton proposes representing these interpretations using structural descriptions, which are small graphs that describe the structure of a scene. These descriptions can vary depending on how the scene is parsed.
Viewpoint Information: Structural descriptions can be associated with viewpoint information, describing the relationship between the object’s intrinsic coordinate frame and the viewer’s frame of reference.
Mental Images and Structural Descriptions: Hinton initially believed that mental images were entirely structural descriptions with viewpoint information. He later refined this view, acknowledging that mental images are more complex and may involve other factors.
Challenges for Neural Networks: Real neural networks face challenges in representing structural descriptions due to their inability to dynamically allocate memory. Hinton investigates how neural networks can represent parse trees in a more plausible way for real neural networks.
00:10:15 Recent Advances in Computer Vision: Transformers, Contrastive Self-supervised Learning,
Transformers: Transformers are a type of neural network architecture that uses attention mechanisms to process data. Attention allows the model to focus on specific parts of the input data, making it more efficient and effective. In natural language processing, transformers have shown significant improvements in tasks such as predicting the next word in a sequence.
Contrastive Self-Supervised Learning: Contrastive self-supervised learning is a technique that involves training a neural network to find spatial coherence in images. The model is shown two different patches of the same image and trained to make the outputs of the neural networks either be the same or be linearly related to each other. This helps the model to extract variables that are spatially coherent and identify meaningful features in images.
Potential of Transformers and Contrastive Self-Supervised Learning: Transformers have the potential to revolutionize computer vision by enabling models to process visual data more efficiently and effectively. Contrastive self-supervised learning can help models learn to find spatial coherence in images, which is a crucial step for many computer vision tasks. Combining these two techniques could lead to significant advancements in computer vision, such as improved object recognition, scene understanding, and image generation.
Introduction to Contrastive Learning of Representations: Contrastive learning aims to extract representations from images useful for classifying objects. By applying deformations and color balance changes to image patches, the system encourages the network to learn meaningful representations. Projecting the representations to lower dimensions and maximizing agreement between them helps the network distinguish between similar and dissimilar patches.
Glom System Overview: Glom is a proposed system designed to overcome limitations in contrastive learning. It aims to achieve agreement between representations only when they satisfy a part-whole hierarchy, ensuring that different objects within the same image have distinct representations. Glom addresses the issue of patches with different objects having similar representations in contrastive learning.
Outer Loop of Vision: Disclaimer: The outer loop of vision involves a sequence of intelligently chosen fixations, which Glom does not currently address.
00:26:12 Artificial Neural Networks for Image Processing
Avoiding the Complexity of Sequential Control: The talk focuses on what happens during the first fixation when processing an image, ignoring sequential control. It assumes a uniform image resolution for simplicity.
Representing Part-Whole Hierarchies: Symbolic AI and computer science approaches allocate neurons for nodes and use pointers or hash tables to connect them. This involves dynamic allocation of memory.
Capsule Models: Capsule models allocate pieces of neural hardware in advance for all possible objects and parts in all possible regions. Each image activates one capsule, which is then dynamically connected to other capsules through a process called dynamic routing. This approach has shown promise for understanding simple images but struggles with large images.
GLOM: GLOM is another method for representing part-whole hierarchies in neural networks.
00:29:08 Biological Inspiration for the GLOM Neural Network
GLOM Overview: GLOM (Global and Local Optimization Machine) uses islands of agreement to represent the power stream, eliminating the need for dynamic allocation. Inspired by biology, where every cell contains the complete instructions for how to make proteins, allowing for parallelism and adaptation to the environment.
DNA and Protein Expression Analogy: The weights of the neural network are analogous to DNA, containing instructions for how to process information. The vector of neural activities of all the cells that look at the same location in the image is like the vector of protein expressions in a cell.
Layers and Levels in Glom: Glom distinguishes between layers and levels of representation. Layers are physical structures in the neural network, while levels represent the complexity of the information being processed. In Glom, each layer can contain multiple levels of representation, allowing for efficient processing of complex information.
00:31:59 Embedding Locations in Vision Transformers
Overview: Each location in a visual scene has an embedding vector, similar to a word embedding in natural language processing. As the network processes the scene, the embedding vector for each location is refined, similar to how a word embedding is refined as it passes through a transformer network.
Embedding Vectors: Each location has an embedding vector that consists of multiple levels of representation. These multiple levels correspond to different levels in the part-whole hierarchy. For example, a location might have an embedding vector for the scene level, the object level, and the part level.
Refining Embedding Vectors: As the network processes the scene, the embedding vectors for each location are refined. The goal is for the embedding vectors to become more specific and accurate as the network learns. For example, the part-level embedding vector for a location might initially be a mess, but after processing, it would become specific to a particular part, such as a nose or a mouth.
Consistency of Embedding Vectors: Locations that are part of the same object or part will have the same embedding vector at the corresponding level. For example, all locations that are part of the same face will have the same embedding vector at the object level.
Determining the Scene Vector: The embedding vector for the scene level is not determined automatically. It is a question of what the scene vector should represent.
00:35:19 Understanding Parse Tree Representation through Identity of Activity Vectors
Visualizing Embeddings: For each location in the image, an embedding is used to capture information such as the type of object, its pose relative to the camera, and other details. These high-dimensional embeddings are represented as 2D vectors for visualization purposes.
Hierarchical Representation: At the lowest level, each location has a unique embedding. As we move up the hierarchy, embeddings from different locations may become identical if they belong to the same sub-part or object. This identity of activity vectors is used to define how things are bound together and to represent the parse tree.
Levels of Representation: The parse tree is represented by the identity of activity vectors at different levels. At the object level, all locations belonging to the same object have the same vector. At the part level, locations belonging to different parts of the object have different vectors.
Interactions Between Levels: In a transformer with multiple heads, all heads interact with each other at each level. However, in this approach, levels only interact with neighboring levels. This helps maintain sensible levels of representation in a part-whole hierarchy.
Embedding Dependency: The embedding at location X in level L depends on the embeddings in the previous layer.
00:38:05 Top-Down and Bottom-Up Interactions in Neural Networks
Level Embeddings and Contributions: Each location X has an embedding at different levels L, L-1, …, N+1. Embeddings at level L depend on embeddings at level L-1 in the previous layer. Parts at level L-1 can predict pose and type of parts at level L. Predictions from different locations should agree for a coherent object.
Top-Down and Bottom-Up Contributions: Top-down contributions come from higher layers (lower levels) making predictions based on high-level representations. Bottom-up contributions come from lower layers (higher levels) making predictions based on local features. Level L embedding receives contributions from level L-1 embedding below, and from level L+1 embedding above. Contributions also include predictions from other level L representations at different locations.
Example with Faces and Noses: Level L-1 nose embedding can predict pose and type of level L face embedding. Level L+1 face embedding can predict location of level L nose embedding. To predict different parts of the face (nose, mouth, etc.) from the same level L+1 face embedding, the location is also considered.
00:43:13 Implicit Functions and Transformers in Computer Vision
Implicit Functions in Computer Vision: Implicit functions are used to predict different things at different locations using the same code vector. The top-down predictive model gets to see the location and can use it to predict different things for different locations. This allows us to use the same vector to predict what’s at many different locations.
Interactions Between Things at the Same Level: In a transformer, the query, key, and value are all the same. The influence from other locations at the same level is proportional to the exponential of the scale of product with what’s at those other locations. This causes the level L embeddings to tend to form islands of similar embeddings.
Training the System: The whole system can be trained as a deep autoencoder. The input is an image with missing regions, and the output is the bottom-level embedding.
00:47:47 Novel Neural Network Architecture for Part-Whole Representation
Transformers and Contrastive Self-Supervised Learning: Transformers are used in language models like BERT to fill in missing regions in an image by training the model to predict the missing parts. Adding contrastive learning to this process helps create explicit representations of the part-whole hierarchy, as the model tries to agree with other vectors at the same level, leading to consensus embeddings. The bottom-up and top-down predictions try to agree with the consensus embedding, resulting in similar embeddings for nearby locations and objects.
Implicit Functions for Graphics: Replicating object embeddings at multiple locations within an object may seem wasteful, but it is beneficial during the search process. It provides multiple places to make hypotheses about grouping and allows for long-range interactions at high levels, where sparse connectivity is sufficient due to the presence of big islands of identical vectors.
Combining Advances for Part-Whole Hierarchy Representation: Hinton proposes combining transformers, contrastive self-supervised learning, and implicit functions for graphics to solve the problem of representing part-whole hierarchies in neural networks. This approach aims to achieve visual representations similar to those used by humans.
Challenges and Future Directions: Most AI researchers are not interested in solving the problem of representing part-whole hierarchies without dynamic storage allocation. Hinton encourages more focus on understanding human cognitive processes and how neural networks can replicate them. The talk’s content will be available online soon, followed by an archive paper.
00:53:15 Concepts of Multi-Level Embeddings and Transformers in Image Processing
How Neural Networks Process Images: Neural networks process images through a series of successive layers. The bottom-up and top-down neural networks perform complex coordinate transformations to predict relationships between different parts of an image. Interactions between embeddings at the same level are like interactions in a transform, where they occur between different locations.
Attention-Weighted Averaging in Transformers: Transformers use attention-weighted averaging to combine similar things. This averaging leads to the formation of groups of identical views that are distinct from other groups.
Determining Locations in an Image: To process an image using transformers, it can be divided into patches (e.g., 8×8). Each patch represents a location in the image. Transformers can be applied to images by dividing the image into patches.
Agreement and Disagreement in Embeddings: Embeddings for related people in the same image may be similar but not identical. At higher levels, there may be a single object representing a pair of people, with identical embeddings for both individuals. Location information allows the neural network to distinguish between the two individuals in the pair.
Separation of Embeddings into Different Levels: The lowest level of embeddings is derived directly from the image and closely resembles pixels. As you move to higher levels, embeddings become more abstract and represent more complex characteristics. The island growing objective promotes the formation of larger islands of identity at higher levels.
00:58:53 Challenges in Implementing GLOM Architecture
Implementation Challenges: Creating an “echo chamber” effect where bottom-up and top-down predictions agree on nearby locations. Representing coordinate transforms in the bottom-up and top-down neural nets. The coordinate transform between a hole and a part depends on the hole’s type, making the neural network more complex.
Addressing Patch Similarity in Sinclair: Use attention to focus on patches with similar features and ignore dissimilar ones. Weight the desire to agree with things that are already similar and avoid making dissimilar things more similar.
Verifying Semantics of Part-Whole Hierarchies: Differentiate between the ISA hierarchy (e.g., mammals are animals) and the part-whole hierarchy (e.g., a nose is part of a face). The part-whole hierarchy is about physical components, while the ISA hierarchy is about class relationships.
01:05:20 Neural Networks for Understanding Part-Whole Hierarchies in Images
Geoffrey Hinton’s Concluding Thoughts: Geoffrey Hinton emphasizes the need to verify the semantics of part-whole hierarchies using neural networks. He proposes examining “islands of agreement” within the network, where regions are segmented together and progressively expand at higher network levels. Hinton also emphasizes the significance of exploring whether the same neural network can generate diverse interpretations or “parses” of the same image, similar to the example of the six rods with two different groupings.
Shaurya Roy’s Concluding Remarks: Shaurya Roy expresses gratitude to Geoffrey Hinton for presenting fresh and timely research insights. He acknowledges that the discussion exceeded the allocated time but highlights the value of the clarifications and questions raised during the session. Roy thanks Hinton for his willingness to engage in the discussion and for sharing his expertise.
Geoffrey Hinton’s Response: Hinton expresses his appreciation for the questions and comments, acknowledging their usefulness in clarifying concepts. He extends his gratitude to the audience for their participation.
In the rapidly evolving field of computer vision, Geoffrey Hinton, a pivotal figure in AI, has made groundbreaking contributions with his research on backpropagation, neural networks, and the visionary Glom system. This comprehensive analysis delves into Hinton’s transformative work, including his revolutionary ideas in speech recognition, object classification, and a novel vision system inspired by human perception. It also explores the cutting-edge advancements in transformers for vision, contrastive self-supervised learning, and the challenges of representing complex part-whole hierarchies, offering a glimpse into the future of image processing and AI.
Main Ideas and Developments:
Geoffrey Hinton’s Contributions to AI and Vision Systems:
Geoffrey Hinton has been a transformative figure in the world of artificial intelligence, particularly in the realm of vision systems. His pioneering introduction of backpropagation has been a cornerstone in neural network research. Hinton’s extensive work encompasses significant contributions such as the development of Boltzmann machines, the advancement of deep learning, and notable innovations in speech recognition and object classification. He has put forth a novel vision system, drawing inspiration from human perception, particularly in how it deals with part-whole hierarchies and coordinate frames. His extensive background in AI, neural networks, and deep learning has been instrumental in his research and subsequent advancements in the field. Hinton’s numerous prestigious awards and recognitions underscore his remarkable contributions to artificial intelligence.
The Role of Coordinate Frames in Perception:
In his exploration of perception, Hinton emphasizes the use of coordinate frames to understand and describe objects, reminiscent of the wireframe cube example. This approach underlines that different perceptions of the same object can lead to a variety of structural descriptions, thereby adding complexity to neural network representations. In a keynote talk, Hinton shed light on his current focus, which involves the synthesis of recent advances in neural network research to develop a new vision system akin to human perception. Despite acknowledging the system’s hypothetical nature, Hinton remains confident in its potential functionality.
Transformers in Vision and Attention Mechanism:
Transformers, initially designed for natural language processing, are now being adapted for tasks in computer vision. They incorporate an attention mechanism that allows them to focus on relevant parts of an image, representing words through query, key, and value vectors for a more nuanced contextual understanding. The potential of transformers to revolutionize computer vision is significant, promising more efficient and effective visual data processing. The integration of these techniques could lead to major advancements in computer vision fields such as enhanced object recognition, scene understanding, and image generation.
Contrastive Self-Supervised Learning and Its Applications:
Contrastive self-supervised learning, a method aiming to find spatial coherence in images, utilizes two neural networks with identical weights to analyze different patches of an image. The SimClear model is a prime example of this approach’s success in image representation. This technique trains a neural network to discern spatial coherence in images, showing the model two different patches of the same image and training it to either align the outputs of the neural networks or relate them linearly. This process enables the model to extract spatially coherent variables and identify meaningful features in images. Each location in a visual scene has an embedding vector, akin to a word embedding in natural language processing. As the network processes the scene, the embedding vector for each location is refined, paralleling the refinement of a word embedding as it progresses through a transformer network.
Challenges in Neural Networks and Representation of Parse Trees:
Traditional neural networks face challenges with dynamic memory allocation, which poses difficulties in representing parse trees. The pursuit to develop neural networks that can accurately represent parse trees, given the limitations of real neural networks, remains a significant challenge. Hinton’s research delves into how neural networks can more plausibly represent parse trees. He proposes using “islands of coherence” for each location in an image, where an embedding captures information such as the type of object, its pose relative to the camera, and other details. These high-dimensional embeddings, while represented as 2D vectors for visualization, hold crucial information for understanding visual scenes.
Future Directions in Computer Vision:
The combination of transformers and contrastive self-supervised learning has led to improvements in image representations. Current research is exploring their integration with other technologies like Generative Adversarial Networks (GANs) for enhanced image generation and manipulation. Hinton envisions the future of computer vision as a synthesis of recent advances in neural network research, combining transformers and contrastive self-supervised learning to create a vision system that mimics human perception. Such a system would offer a more natural and efficient way to understand and interpret visual information.
Glom: An Innovative Approach to Part-Whole Hierarchies:
Glom addresses the limitations inherent in contrastive learning by facilitating agreement between patch representations that satisfy part-whole hierarchies. This approach uses “islands of agreement” and is inspired by the redundancy and parallelism observed in cellular DNA. Glom operates with multi-level embeddings for image recognition, where each location X has an embedding at different levels, and embeddings at one level depend on those at the previous level. This allows parts at a lower level to predict the pose and type of parts at a higher level. For a coherent object, predictions from different locations should be in agreement.
Sampling and Goal-Directed Perception in Visual Processing:
Visual perception involves a selective sampling of information tailored for specific tasks, akin to a magician’s art of misdirection. The human visual system processes input at a low resolution, focusing on specific areas during each fixation. In this process, top-down contributions come from higher layers, making predictions based on high-level representations, while bottom-up contributions originate from lower layers, based on local features. The level L embedding receives contributions from both the level L-1 embedding below it and the level L+1 embedding above it, as well as from other level L representations at different locations.
Implementing Part-Whole Hierarchies in AI:
Traditional AI approaches use dynamic memory for hierarchical structures, whereas capsule models pre-allocate neural hardware. GLOM offers an alternative approach, with dedicated neural cells for specific image parts, distinguishing between layers and levels of representation. This method proposes a more structured and dedicated approach to part-whole hierarchies.
Complexities and Challenges in Network Interactions:
The interaction between levels in neural networks is intricate, involving a mix of bottom-up and top-down predictions. A key ongoing challenge is verifying the semantics of part-whole hierarchies in neural networks and distinguishing between different types of hierarchies. For example, in the context of facial recognition, a lower-level nose embedding can predict the pose and type of a higher-level face embedding, and vice versa, with the higher-level face embedding predicting the location of the nose embedding at a lower level.
The Future of
Vision and AI
In conclusion, Geoffrey Hinton’s work has laid a foundational framework for the future of computer vision, presenting innovative approaches and challenges that continue to shape the field. The integration of transformers, self-supervised learning, and novel concepts like Glom are pushing the boundaries of image processing and AI. As research progresses, these advancements promise to further our understanding of vision systems, both artificial and biological, and open new avenues for technological innovation. The potential for these technologies to transform our approach to computer vision is immense, highlighting a future where AI can process and understand visual information with a sophistication akin to human perception.
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