Wang, LiangweiWang, ZhanXiao, ShishiLiu, LeTsung, FugeeZeng, WeiAigner, WolfgangAndrienko, NataliaWang, Bei2025-05-262025-05-2620251467-8659https://doi.org/10.1111/cgf.70110https://diglib.eg.org/handle/10.1111/cgf70110Comprehending visualizations requires readers to interpret visual encoding and the underlying meanings actively. This poses challenges for visualization novices, particularly when interpreting distributional visualizations that depict statistical uncertainty. Advancements in LLM-based conversational interfaces show promise in promoting visualization comprehension. However, they fail to provide contextual explanations at fine-grained granularity, and chart readers are still required to mentally bridge visual information and textual explanations during conversations. Our formative study highlights the expectations for both lexical and visual feedback, as well as the importance of explicitly linking these two modalities throughout the conversation. The findings motivate the design of VIZTA, a visualization teaching assistant that leverages the fusion of visual and lexical feedback to help readers better comprehend visualization. VIZTA features a semantic-aware conversational agent capable of explaining contextual information within visualizations and employs a visual-lexical fusion design to facilitate chart-centered conversation. A between-subject study with 24 participants demonstrates the effectiveness of VIZTA in supporting the understanding and reasoning tasks of distributional visualization across multiple scenarios.Attribution 4.0 International LicenseCCS Concepts: Human-centered computing → Visualization systems and toolsHuman centered computing → Visualization systems and tools10.1111/cgf.7011012 pages