UTS at PsyDefDetect: Multi-Agent Councils and Absence-Based Reasoning for Defense Mechanism Classification

Dima Galat, Marian Rizoiu


Abstract
This paper describes our system for classifying psychological defense mechanisms in emotional support dialogues using the Defense Mechanism Rating Scales (DMRS), placing second (F1 0.406) among 64 teams.1 A central insight is that defense mechanisms are defined by what is absent: missing affect, blocked cognition, denied reality. We encode this as an affect-cognition integration spectrum in prompt-level clinical rules, which account for the largest single gain (+11.4pp F1).Our architecture is a multi-phase deliberative council of Gemini 2.5 agents where class-specific advocates rate evidence strength rather than voting, achieving F1 0.382 with no fine-tuning - a top-5 result on its own. We find, however, that the council is confidently wrong about minority classes: 59–80% of stable minority predictions are incorrect, driven by a systematic "L7 attractor" in which emotional content defaults to the majority class. A targeted override ensemble from three fine-tuned Qwen3.5 models applies 16 overrides (+2.4pp), selected by a structured multi-agent system (builder, critic, regression guard) that produced a larger F1 gain in one iteration than 8 prior attempts combined.
Anthology ID:
2026.bionlp-2.6
Volume:
Proceedings of the BioNLP 2026 (Shared Tasks)
Month:
July
Year:
2026
Address:
San Diego, California, USA
Editors:
Deepak Gupta, Dina Demner-Fushman
Venues:
BioNLP | WS
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Publisher:
Association for Computational Linguistics
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Pages:
38–46
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URL:
https://preview.aclanthology.org/ingest-acl-workshops/2026.bionlp-2.6/
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Cite (ACL):
Dima Galat and Marian Rizoiu. 2026. UTS at PsyDefDetect: Multi-Agent Councils and Absence-Based Reasoning for Defense Mechanism Classification. In Proceedings of the BioNLP 2026 (Shared Tasks), pages 38–46, San Diego, California, USA. Association for Computational Linguistics.
Cite (Informal):
UTS at PsyDefDetect: Multi-Agent Councils and Absence-Based Reasoning for Defense Mechanism Classification (Galat & Rizoiu, BioNLP 2026)
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https://preview.aclanthology.org/ingest-acl-workshops/2026.bionlp-2.6.pdf
Supplementarymaterial:
 2026.bionlp-2.6.SupplementaryMaterial.txt
Supplementarymaterial:
 2026.bionlp-2.6.SupplementaryMaterial.zip