The goal of this observational study is to learn how severe obstructive sleep apnea-hypopnea syndrome (OSAHS) affects the brain's ability to process sounds and attention in adults aged 20-60 years. The main questions it aims to answer are: 1. Does severe OSAHS change how the brain automatically detects sound changes during wakefulness? 2. Does severe OSAHS reduce people's ability to pay attention to important sounds when awake? 3. Can brainwave tests (Electroencephalogram, EEG) detect early signs of hearing-related cognitive problems in OSAHS patients before symptoms appear? Researchers will compare two groups: * 50 adults with severe OSAHS (diagnosed by sleep tests) * 50 healthy adults matched by age and gender Participants will: * Complete hearing tests (MoCA) * Undergo a 1-night sleep test (PSG) * Wear an EEG cap for 1.5-2 hours while listening to sounds in a quiet room: * Passive task: Relax (no response needed) * Active task: Press a button when hearing rare sounds * Receive ¥75/hour compensation for their time