TechTalks from event: ICML 2011
Active and Online Learning
Speeding-Up Hoeffding-Based Regression Trees With OptionsData streams are ubiquitous and have in the last two decades become an important research topic. For their predictive non-parametric analysis, Hoeffding-based trees are often a method of choice, offering a possibility of any-time predictions. However, one of their main problems is the delay in learning progress due to the existence of equally discriminative attributes. Options are a natural way to deal with this problem. Option trees build upon regular trees by adding splitting options in the internal nodes. As such they are known to improve accuracy, stability and reduce ambiguity. In this paper, we present on-line option trees for faster learning on numerical data streams. Our results show that options improve the any-time performance of ordinary on-line regression trees, while preserving the interpretable structure of trees and without significantly increasing the computational complexity of the algorithm.
Adaptively Learning the Crowd KernelWe introduce an algorithm that, given n objects, learns a similarity matrix over all n^2 pairs, from crowdsourced data *alone*. The algorithm samples responses to adaptively chosen triplet-based relative-similarity queries. Each query has the form "is object a more similar to b or to c?" and is chosen to be maximally informative given the preceding responses. The output is an embedding of the objects into Euclidean space (like MDS); we refer to this as the "crowd kernel." SVMs reveal that the crowd kernel captures prominent and subtle features across a number of domains, such as "is striped" among neckties and "vowel vs. consonant" among letters.
Bundle Selling by Online Estimation of Valuation FunctionsWe consider the problem of online selection of a bundle of items when the cost of each item changes arbitrarily from round to round and the valuation function is initially unknown and revealed only through the noisy values of selected bundles (the bandit feedback setting). We are interested in learning schemes that have a small regret compared to an agent who knows the true valuation function. Since there are exponentially many bundles, further assumptions on the valuation functions are needed. We make the assumption that the valuation function is supermodular and has non-linear interactions that are of low degree in a novel sense. We develop efficient learning algorithms that balance exploration and exploitation to achieve low regret in this setting.
Active Learning from CrowdsObtaining labels is expensive or time-consuming, but unlabeled data is often abundant and easy to obtain. Many learning task can profit from intelligently choosing unlabeled instances to be labeled by an oracle also known as active learning, instead of simply labeling all the data or randomly selecting data to be labeled. Supervised learning traditionally relies on an oracle playing the role of a teacher. In the multiple annotator paradigm, an oracle, who knows the ground truth, no longer exists; instead, multiple labelers, with varying expertise, are available for querying. This paradigm posits new challenges to the active learning scenario. We can ask which data sample should be labeled next and which annotator should we query to benefit our learning model the most. In this paper, we develop a probabilistic model for learning from multiple annotators that can also learn the annotator expertise even when their expertise may not be consistently accurate (or inaccurate) across the task domain. In addition, we provide an optimization formulation that allows us to simultaneously learn the most uncertain sample and the annotator/s to query the labels from for active learning. Our active learning approach combines both intelligently selecting samples to label and learning from expertise among multiple labelers to improve learning performance.