When Models Hear What They Expect: Diagnosing Prosodic Heuristics in Multimodal Sarcasm Detection

Yongjian Chen, Pengfei Wei, Yiqun Sun, Zhu Li, Lawrence B. Hsieh


Abstract
Multimodal Large Language Models (MLLMs) process speech and text jointly, yet whether they exploit prosodic cues for pragmatic inference or rely on surface acoustic patterns has received little systematic investigation. We address this through sarcasm detection, evaluating Qwen2.5-Omni and Qwen3-Omni on Mandarin Chinese and English under five modality conditions that decompose the contributions of lexical content, vocal semantics, and prosodic structure. Adding audio systematically inflates false positives without improving true positive detection. Acoustic error diagnosis reveals that model errors cluster on a shared stereotype of expressive prosody, namely elevated pitch and irregular pausing, that diverges from the actual cues marking sarcasm in both languages. Targeted manipulation of only these two dimensions causally confirms the heuristic, inducing false positive rates of up to 60%. Applying the same manipulation template to Gemini 3 Flash Preview without modification replicates the effect, suggesting that the stereotype extends beyond the Qwen Omni family rather than arising from a single model architecture.
Anthology ID:
2026.findings-emnlp.1464
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
31162–31181
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1464/
DOI:
Bibkey:
Cite (ACL):
Yongjian Chen, Pengfei Wei, Yiqun Sun, Zhu Li, and Lawrence B. Hsieh. 2026. When Models Hear What They Expect: Diagnosing Prosodic Heuristics in Multimodal Sarcasm Detection. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 31162–31181, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
When Models Hear What They Expect: Diagnosing Prosodic Heuristics in Multimodal Sarcasm Detection (Chen et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1464.pdf