The paper introduces and formalizes the problem of missing modalities in multimodal recommendation, where a portion of items in the catalogue lack multimodal content (e.g., product images, textual descriptions) to extract meaningful features from. To address this issue, the authors propose to reshape the missing modalities problem as a problem of missing graph node features, and leverage the state-of-the-art FeatProp algorithm to impute the missing multimodal features.
Specifically, the authors first project the user-item bipartite graph into an item-item co-interaction graph, based on the assumption that co-interacted items share similar multimodal content. Then, they apply a modified version of the FeatProp algorithm to propagate the available multimodal features and impute the missing ones. The reconstructed multimodal features are finally used as input to power any multimodal recommender system.
The authors conduct an extensive experimental evaluation, comprising 1080 settings across 3 recommendation datasets, 2 multimodal recommender systems, 4 methods to impute missing modalities, and 9 percentages of missing items. The results show that FeatProp consistently outperforms other shallower baselines, especially when the percentage of missing items is not too high. Additionally, the authors investigate the impact of the number of propagation layers, finding that not all multimodal recommender systems may require the same number of layers to converge.
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