jmlr jmlr2011 jmlr2011-55 knowledge-graph by maker-knowledge-mining

55 jmlr-2011-Learning Multi-modal Similarity


Source: pdf

Author: Brian McFee, Gert Lanckriet

Abstract: In many applications involving multi-media data, the definition of similarity between items is integral to several key tasks, including nearest-neighbor retrieval, classification, and recommendation. Data in such regimes typically exhibits multiple modalities, such as acoustic and visual content of video. Integrating such heterogeneous data to form a holistic similarity space is therefore a key challenge to be overcome in many real-world applications. We present a novel multiple kernel learning technique for integrating heterogeneous data into a single, unified similarity space. Our algorithm learns an optimal ensemble of kernel transformations which conform to measurements of human perceptual similarity, as expressed by relative comparisons. To cope with the ubiquitous problems of subjectivity and inconsistency in multimedia similarity, we develop graph-based techniques to filter similarity measurements, resulting in a simplified and robust training procedure. Keywords: multiple kernel learning, metric learning, similarity

Reference: text


Summary: the most important sentenses genereted by tfidf model

sentIndex sentText sentNum sentScore

1 We present a novel multiple kernel learning technique for integrating heterogeneous data into a single, unified similarity space. [sent-8, score-0.508]

2 Our algorithm learns an optimal ensemble of kernel transformations which conform to measurements of human perceptual similarity, as expressed by relative comparisons. [sent-9, score-0.426]

3 Keywords: multiple kernel learning, metric learning, similarity 1. [sent-11, score-0.489]

4 In some cases, a natural notion of similarity may emerge from domain knowledge, for example, cosine similarity for bag-of-words models of text. [sent-13, score-0.572]

5 For example, if the corpus consists of musical data, each song or artist may be represented simultaneously by acoustic features (such as rhythm and timbre), semantic features (tags, lyrics), or social features (collaborative filtering, artist reviews and biographies, etc). [sent-16, score-0.686]

6 In such cases, there is generally no obvious way to combine representations to form a unified similarity space which optimally integrates heterogeneous data. [sent-18, score-0.415]

7 , Euclidean distance in Rd ), and the problem of optimizing similarity reduces to finding a suitable embedding of the data under a specific choice of the distance metric. [sent-25, score-0.799]

8 Once a suitable metric has been learned, similarity to new, unseen data can be computed either directly (if the metric takes a certain parametric form, for example, a linear projection matrix), or via out-of-sample extensions (Bengio et al. [sent-36, score-0.477]

9 To guide the construction of a similarity space for multi-modal data, we adopt the idea of using similarity measurements, provided by human labelers, as side-information. [sent-38, score-0.572]

10 Thus, rather than rely on quantitative similarity or hard binary labels of pairwise similarity, it is now becoming increasingly common to collect similarity information in the form of triadic or relative comparisons (Schultz and Joachims, 2004; Agarwal et al. [sent-42, score-0.732]

11 ” Although this form of similarity measurement has been observed to be more stable than quantitative similarity (Kendall and Gibbons, 1990), and clearly provides a richer representation than binary pairwise similarities, it is still subject to problems of consistency and inter-labeler agreement. [sent-44, score-0.572]

12 In the present work, our goal is to develop a framework for integrating multi-modal data so as to optimally conform to perceptual similarity encoded by relative comparisons. [sent-46, score-0.536]

13 The algorithm must be able to integrate multi-modal data in an optimal way, that is, the distances between embedded points should conform to perceptual similarity measurements. [sent-50, score-0.567]

14 Humans supply perceptual similarity measurements in the form of relative pairwise comparisons, which are in turn filtered by graph processing algorithms, and then used as constraints to optimize the multiple kernel embedding. [sent-55, score-0.759]

15 This type of embedding problem has been previously studied by Agarwal et al. [sent-57, score-0.427]

16 (2007) provide no out-of-sample extension, and neither support heterogeneous feature integration, nor do they address the problem of noisy similarity measurements. [sent-60, score-0.412]

17 However, none of these methods specifically address the problem of learning a unified data representation which conforms to perceptual similarity measurements. [sent-69, score-0.451]

18 First, we develop the partial order embedding (POE) framework (McFee and Lanckriet, 2009b), which allows us to use graph-theoretic algorithms to filter a collection of subjective similarity measurements for consistency and redundancy. [sent-72, score-0.906]

19 We then formulate a novel multiple kernel learning (MKL) algorithm which learns an ensemble of feature space projections to produce a unified similarity space. [sent-73, score-0.468]

20 Our method is able to produce non-linear embedding functions which generalize to unseen, out-of-sample data. [sent-74, score-0.427]

21 In Section 3, we derive an embedding algorithm which learns an optimal transformation of a single feature space. [sent-78, score-0.47]

22 In Section 4, we develop a novel multiple-kernel learning formulation for embedding problems, and derive an algorithm to learn an optimal space from heterogeneous data. [sent-79, score-0.51]

23 Section 5 provides experimental results illustrating the effects of graph-processing on noisy similarity data, and the effectiveness of the multiple-kernel embedding algorithm on a music similarity task with human 493 M C F EE AND L ANCKRIET perception measurements. [sent-80, score-1.045]

24 A Euclidean embedding is a function g : X → Rd which maps X into a d-dimensional space equipped with the Euclidean (ℓ2 ) metric: x−y 2 = (x − y)T (x − y). [sent-92, score-0.427]

25 A Graphical View of Similarity Before we can construct an embedding algorithm for multi-modal data, we must first establish the form of side-information that will drive the algorithm, that is, the similarity measurements that will be collected from human labelers. [sent-105, score-0.796]

26 Unlike classical or metric MDS techniques, which seek to preserve quantitative distances, NDMS seeks an embedding in which the rank-ordering of distances is preserved. [sent-113, score-0.566]

27 Since NMDS only needs the rank-ordering of distances, and not the distances themselves, the task of collecting similarity measurements can be simplified by asking test subjects to order pairs of points by similarity: “Are i and j more similar than k and ℓ? [sent-114, score-0.444]

28 ” Based on this kind of relative comparison data, the embedding problem can be formulated as follows. [sent-116, score-0.473]

29 ) The goal is to find an embedding function g : X → Rd such that ∀(i, j, k, ℓ) ∈ C : g(i) − g( j) 2 + 1 < g(k) − g(ℓ) 2 . [sent-119, score-0.427]

30 (2007) work with this kind of relative comparison data and describe a generalized NMDS algorithm (GNMDS), which formulates the embedding problem as a semi-definite program. [sent-122, score-0.473]

31 1, we develop a graphical framework to infer and interpret the global structure exhibited by the constraints of the embedding problem. [sent-128, score-0.475]

32 The final, reduced set of relative comparison constraints defines a partial order, making for a more robust and efficient embedding problem. [sent-131, score-0.593]

33 If C contains cycles, then there exists no embedding which can satisfy C . [sent-138, score-0.427]

34 If C is acyclic, any embedding that satisfies the transitive reduction C min also satisfies C . [sent-140, score-0.506]

35 The first fact implies that no algorithm can produce an embedding which satisfies all measurements if the graph is cyclic. [sent-141, score-0.552]

36 In fact, the converse of this statement is also true: if C is acyclic, then an embedding exists in which all similarity measurements are preserved (see Appendix A). [sent-142, score-0.796]

37 These two observations allude to two desirable properties in C for embedding methods: transitivity and anti-symmetry. [sent-147, score-0.427]

38 2 Graph Simplification Because a set of similarity measurements C containing cycles cannot be embedded in any Euclidean space, C is inherently inconsistent. [sent-152, score-0.417]

39 In the graph view of similarity measurements, redundancies can be easily removed by computing the transitive reduction of the graph (Aho et al. [sent-163, score-0.449]

40 Additionally, pruning the constraint set by transitive reduction focuses embedding algorithms on the most important core set of constraints while reducing overhead due to redundant information. [sent-167, score-0.554]

41 Partial Order Embedding Now that we have developed a language for expressing similarity between items, we are ready to formulate the embedding problem. [sent-169, score-0.713]

42 In this section, we develop an algorithm that learns a representation of data consistent with a collection of relative similarity measurements, and allows to map unseen data into the learned similarity space after learning. [sent-170, score-0.654]

43 By parameterizing the embedding function g in terms of the feature representation, we will be able to apply g to any point in the feature space, thereby generalizing to data outside of the training set. [sent-172, score-0.552]

44 There are of course many ways to define an embedding function g : RD → Rd . [sent-175, score-0.427]

45 After learning M by solving this optimization problem, the embedding can be extended to out-ofsample points x′ by applying the projection: x′ → Mx′ . [sent-187, score-0.427]

46 Finally, after the optimal W is found, the embedding function g : RD → RD can be recovered from the spectral decomposition of W : W = V ΛV T ⇒ g(x) = Λ1/2V T x, and a d-dimensional approximation can be recovered by taking the leading d eigenvectors of W . [sent-193, score-0.427]

47 Algorithm 2 Linear partial order embedding (LPOE) Input: n objects X , partial order C , data matrix X ∈ RD×n , β>0 Output: mapping g : X → Rd min tr (W ) + W,ξ β |C | ∑ C ξi jkℓ . [sent-194, score-0.675]

48 The embedding function g : X → Rd is the therefore the composition of the projection M with φ: g(x) = M(φ(x)). [sent-197, score-0.49]

49 Because φ may be non-linear, this allows us to learn a non-linear embedding g. [sent-198, score-0.427]

50 The embedding g can thus be expressed as g(x) = ( ω p , φ(x) H )d , p=1 where (·)d denotes concatenation. [sent-203, score-0.427]

51 (3) We can now reformulate the embedding problem as an optimization over N rather than M. [sent-215, score-0.427]

52 The embedding problem thus amounts to solving the following optimization problem in N and ξ: min N,ξ≥0 s. [sent-219, score-0.427]

53 The resulting embedding problem is listed as Algorithm 3, again a semi-definite programming problem (SDP), with an objective function and constraints that are linear in W . [sent-225, score-0.475]

54 The resulting embedding function takes the form: g(x) = Λ1/2V T Kx . [sent-227, score-0.427]

55 500 (6) L EARNING M ULTI - MODAL S IMILARITY Algorithm 3 Kernel partial order embedding (KPOE) Input: n objects X , partial order C , kernel matrix K, β>0 Output: mapping g : X → Rn min tr (W K) + W,ξ β ξi jkℓ |C | ∑ C . [sent-235, score-0.814]

56 Thus, if C defines a DAG, we could exploit the fact that a partial order over distances always allows an embedding which satisfies all constraints in C (see Appendix A) to eliminate the slack variables from the program entirely. [sent-243, score-0.622]

57 Multiple Kernel Embedding In the previous section, we derived an algorithm to learn an optimal projection from a kernel space H to Rd such that Euclidean distance between embedded points conforms to perceptual similarity. [sent-245, score-0.458]

58 —we can formulate a multiple kernel learning algorithm to optimally combine all feature spaces into a single, unified embedding space. [sent-254, score-0.655]

59 , those which can be transformed to best fit C ) from bad features, and as a result, the quality of the resulting embedding may be degraded. [sent-276, score-0.427]

60 Applying this reasoning to learning an embedding that conforms to perceptual similarity, one might consider a two-stage approach to parameterizing the embedding (Figure 3(a)): first construct a weighted kernel combination, and then project from the combined kernel space. [sent-283, score-1.297]

61 Constraining the embedding to a single metric W with a single weight µ p for each kernel may be too restrictive to take advantage of this phenomenon. [sent-291, score-0.63]

62 Intuitively, by defining the embedding as the concatenation of m different projections, we allow the algorithm to learn an ensemble of 503 M C F EE AND L ANCKRIET projections, each tailored to its corresponding domain space and jointly optimized to produce an optimal space. [sent-298, score-0.465]

63 Mathematically, an embedding function of this form can be expressed as the concatenation g(x) = (M p (φ p (x)))m . [sent-300, score-0.427]

64 p=1 Now, given this characterization of the embedding function, we can adapt Algorithm 3 to optimize over multiple kernels. [sent-301, score-0.427]

65 Again, by invoking the representer theorem for each M p , it follows that M p = N p (Φ p )T , for some matrix N p , which allows to reformulate the embedding problem as a joint optimization over N p , p = 1, . [sent-303, score-0.427]

66 (8) g(x) = (M p (φ p (x)))m = (N p Kxp )m , p=1 p=1 (9) Mp 2 HS = p=1 p=1 The embedding function can now be rewritten as and the inner products between embedded points take the form: m Ai j = g(xi ), g(x j ) = ∑ N p Kip T N p K jp p=1 m = ∑ (Kip )T (N p )T (N p )(K jp ). [sent-311, score-0.581]

67 , µm to form a weighted feature space H ∗ , which is subsequently projected to the embedding space via M. [sent-393, score-0.47]

68 The projections are jointly optimized to produce the embedding space. [sent-395, score-0.465]

69 Algorithm 4 Multiple kernel partial order embedding (MKPOE) Input: n objects X , partial order C , m kernel matrices K 1 , K 2 , . [sent-396, score-0.885]

70 Experiments To evaluate our framework for learning multi-modal similarity, we first test the multiple kernel learning formulation on a simple toy taxonomy data set, and then on a real-world data set of musical perceptual similarity measurements. [sent-412, score-0.64]

71 For 507 M C F EE AND L ANCKRIET each fold, we learned a diagonally-constrained embedding with Algorithm 4, using the subset of relative comparisons (i, j, k, ℓ) with i, j, k and ℓ restricted to the training set. [sent-433, score-0.624]

72 After learning the embedding, the held out data (validation or test) was mapped into the space, and the accuracy of the embedding was determined by counting the fraction of correctly predicted relative comparisons. [sent-434, score-0.473]

73 We repeat this experiment for each base kernel individually (that is, optimizing over K1 with a single base kernel), as well as the unweighted sum kernel (K1 with all base kernels), and finally MKPOE (K4 with all base kernels). [sent-436, score-0.559]

74 The artist similarity problem is motivated by several real-world applications, including recommendation and playlist-generation for online radio. [sent-451, score-0.537]

75 , tags, acoustic features, social data), such applications can benefit greatly from an optimally integrated similarity metric. [sent-454, score-0.453]

76 Relative comparisons were acquired from human test subjects through a web survey; subjects were presented with a query artist (i), and asked to choose what they believe to be the most similar artist ( j) from a list of 10 candidates. [sent-457, score-0.578]

77 The MKL embedding results are presented in Section 5. [sent-466, score-0.427]

78 Finally, the kernel between artists i and j is the probability product kernel (Jebara et al. [sent-492, score-0.467]

79 fm,2 a social music website which allows users to label songs or artists with arbitrary tag words or social tags. [sent-502, score-0.496]

80 The kernel between artists for social tags is the cosine similarity (linear kernel) between TF-IDF vectors. [sent-505, score-0.753]

81 As with social tags, the kernel between artists is the cosine similarity between TF-IDF bag-of-words vectors. [sent-509, score-0.694]

82 The kernel between artists in this view is the cosine of the angle between corresponding rows in the matrix, which can be interpreted as counting the amount of overlap between the sets of users listening to each artist and normalizing for overall artist popularity. [sent-515, score-0.83]

83 ) After training, test artists were mapped into the learned space (by Equation 9), and accuracy was measured by counting the number of measurements (i, j, i, k) correctly predicted by distance in the learned space, where i belongs to the test set, and j, k belong to the training set. [sent-526, score-0.426]

84 9 1 Figure 6: aset400 embedding results for each of the base kernels. [sent-545, score-0.478]

85 ) After finding the best-performing β, the embedding is trained on the full (processed) training set. [sent-551, score-0.466]

86 8 Figure 7: aset400 embedding results with multiple kernel learning: the learned metrics are optimized over K4 by Algorithm 4. [sent-586, score-0.64]

87 The embedding captures a great deal of high-level genre structure: for example, the classic rock and metal genres lie at the opposite end of the space from pop and hiphop. [sent-590, score-0.427]

88 Using each of these variants of the training set, we test the embedding algorithm with both diagonal and full-matrix formulations. [sent-599, score-0.515]

89 04 Table 2: aset400 embedding results (Biography kernel) for three possible refinements of the constraint set. [sent-628, score-0.427]

90 The embedding is constructed by optimizing over K4 with all five base kernels. [sent-641, score-0.478]

91 9 1 Figure 10: Accuracy of the learned embedding for each training/test split, averaged over ten trials with random maximal acyclic constraint subgraphs. [sent-653, score-0.534]

92 It remains to show that the R1 partial order embedding problem (hereafter referred to as 1-POE) is NP-Hard. [sent-665, score-0.499]

93 Since 1-POE can be reduced to the general optimization problem of finding an embedding of minimal dimensionality, we can conclude that dimensionality reduction subject to partial order constraints is also NP-Hard. [sent-674, score-0.547]

94 Table 1 provides a unified perspective of multiple kernel learning formulations for embedding problems, but it is clearly not complete. [sent-684, score-0.566]

95 , a chain graph), the problem reduces to non-metric multidimensional scaling (Kruskal, 1964), and a constraint-satisfying embedding can always be found by the constant-shift embedding algorithm of Roth et al. [sent-691, score-0.91]

96 An embedding can be found by first applying classical multidimensional scaling (MDS) (Cox and Cox, 1994) to ∆: 1 A = − H∆H, 2 where H = I − 1 11T is the n × n centering matrix, and 1 is a vector of 1s. [sent-698, score-0.483]

97 The embedding g can be found by decomposing 1/2 A = V ΛV T , so that g(xi ) is the ith column of Λ V T ; this is the solution constructed by the constantshift embedding non-metric MDS algorithm of Roth et al. [sent-700, score-0.854]

98 Thus, for any instance (X , C ), an embedding can be found in Rn−1 . [sent-704, score-0.427]

99 As noted by Schultz and Joachims (2004), the fraction of relative comparisons satisfied by an embedding g is closely related to the area under the receiver operating characteristic curve (AUC). [sent-726, score-0.549]

100 An embedding which satisfies a complete set of constraints of this form will receive an AUC score of 1, since every relevant point must be closer to xi than every irrelevant point. [sent-736, score-0.534]


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