{
  "meta_info": {
    "case_id": "case39_19",
    "bench_subset": "NeuroBench-Multi",
    "difficult": 1,
    "original_dataset": "Multi_QA"
  },
  "agent_input": {
    "data_path": [],
    "instruction": "Answer this standalone multimodal neurophysiology multiple-choice question: What physiological quantity is detected by photoplethysmography? Options: A: It mechanically measures airflow through the airway. B: It electrically measures skeletal muscle motor units. C: It electrically detects myocardial depolarization. D: It optically detects changes in blood volume within the peripheral microvascular bed. Select exactly one option, A, B, C, or D. Return only one JSON object with the single field answer and no explanation or extra fields."
  },
  "eval_config": {
    "parser_prompt": "### ROLE\nYou are a precise JSON Extraction Engine for neurophysiological data. Your sole task is to convert natural language reports into structured JSON data.\n\n### TASK\nExtract the answer choice from the agent's report.\n- answer: exactly one of A, B, C, or D.\n\n### STRICT CONSTRAINTS (MANDATORY)\n1. Output ONLY a valid JSON object.\n2. DO NOT include Markdown code blocks.\n3. DO NOT include conversational text, explanations, or extra fields.\n4. The JSON key must be EXACTLY \"answer\".\n5. The answer value must be exactly one of \"A\", \"B\", \"C\", or \"D\".\n6. If the answer is missing or unclear, return {\"answer\": null}.\n\n### OUTPUT TEMPLATE\n{\"answer\": \"<A | B | C | D or null>\"}",
    "metrics": [
      {
        "metric_id": "knowledge_answer_accuracy",
        "type": "categorical_check",
        "target_key": "answer",
        "weight": 100,
        "params": {
          "gt_value": "D"
        }
      }
    ]
  }
}