Chapter 271: Thresholds and Noise

At six on Tuesday morning, daylight had not yet fully entered the ward. Lin Chen opened his eyes on time. Overnight, the swelling in his left foot had settled into a dull, heavy soreness; the skin around his ankle was stretched shiny, and the red marks cut by the sock cuff had not yet faded. He slowly sat up, shifted his weight onto his right leg, and held the edge of the bed as he stood. He did not go wash up right away. Instead, he checked the engineering unit first. The voltage reading was 3.51V; downclocked mode was running steadily; in the warning module’s background log, two movement-interference events had been recorded over the past six hours, both correctly filtered. He wrote down the data and set the device back on the bedside cabinet.

At 7:40, in the Information Department of the Municipal Second Hospital, the corridor was filled with the mixed smell of disinfectant and old carpet. The wall paint had peeled at the corner, exposing yellowed cement underneath. Lin Chen handed his ID card, a photocopy of the ethics approval, and the confidentiality agreement through the glass window. The clerk inside was a middle-aged man wearing black-framed glasses. He glanced over the materials, said nothing, and turned toward the inner room to fetch the hard drive. During the twenty-minute wait, Lin Chen leaned against the wall, lightly tapping the floor with his right foot to keep the blood returning. He understood the temperament of hospital data: inconsistent formats, subjective annotations, timestamps that often drifted. Getting the data was only the first step. Cleaning and mapping it would be the real hard fight.

“You have to sign before you can copy it.” The clerk pushed out a thick Data Use Commitment Letter, along with a chipped signing pen. Lin Chen flipped through it page by page, paused for one second at the liability clauses, and signed his name. The USB drive was inserted, and the progress bar climbed slowly. 3.2GB of raw mixed EEG and EMG data. The clerk tapped at his keyboard without lifting his head. “The annotations were done by interns last year. Some artifacts weren’t removed, and the periods when leads fell off weren’t marked either. Use it at your own discretion. Don’t come back later saying there’s a problem with our data.”

“Understood,” Lin Chen said. “We’ll only do desensitization processing. We won’t touch the original medical records.”

When he returned to the ward, Xiaoman had not woken yet. Her breathing was very light, the rise and fall of her chest steady. Lin Chen connected the engineering unit to his laptop and began running the cleaning script. V3.0’s log module automatically recorded every filtering step. The waveform chart on the screen gradually unfurled, like a field of wheat tossed into disorder by the wind. Comparing it against the “gold standard” seizure timestamps provided by the hospital, he found that the warning windows marked by the algorithm were, on average, 4 minutes 17 seconds earlier than the clinical records. It was not an error; the dimensions of feature extraction were different. Clinically, they looked for obvious spike-and-slow waves. The algorithm caught the tiny EMG tremors before onset. Those four minutes were the time a family member could use to prepare a bite guard and adjust body position. They were also the device’s only reason to exist.

He brought up the code and added a segment of interpolation logic to the time-alignment module. Handle missing values, remove 50Hz mains interference, recalibrate the sampling rate. The script ran for forty-seven minutes, the CPU fan giving off a faint hum. Final output: 2,140 valid data entries, confidence threshold 0.82. Lower than expected, but enough to support the demonstration.

At eleven in the morning, Su Man pushed the door open, carrying a silver insulated case. The power modules from the hardware factory had arrived. She skipped the pleasantries and directly opened the antistatic bag, taking out the replacement board. “High-rate cell. Rated cycle life of 800 cycles. I tested the low-temperature power-drop curve; at minus five degrees, it can still maintain 3.5V.” Lin Chen took the module and rechecked the internal resistance with a multimeter. The data matched. He swapped it onto the mainboard and reflashed the firmware. The power-on self-test passed.

The two of them connected the engineering unit to Xiaoman’s spare leads. Su Man watched the real-time waveform, her brow faintly furrowed. “With the 0.3-second delay after downclocking, will it miss high-frequency clusters during REM sleep?”

Lin Chen pulled up the buffer-queue settings. “I added sliding-window preloading. Trade 0.3 seconds of response time for uninterrupted power. What the clinic needs isn’t millisecond-level precision. It’s ‘don’t suddenly shut down in the middle of the night.’”

Su Man was silent for a moment, then nodded. “When we see Director Zhao on Wednesday, explain it with that logic. Don’t compete on parameters; compete on usability. Write clearly what it costs to push the false-positive rate down to 0.41. Don’t let them think we’re hiding defects.”

That afternoon, Lin Chen sliced the cleaned data and imported it into the demo PowerPoint. He deleted all the complicated algorithm-architecture diagrams and left only three charts: a waveform comparison from a clinically missed-alert case, the battery-life curve under the device’s downclocked mode, and a simulation showing the decrease in nurse interventions after the false-positive rate was pushed down to 0.41. He polished the wording again and again, removing terms like “disruptive” and “leading,” replacing them with “supplementary,” “assistive,” and “reduces workload.” He knew that directors at top-tier hospitals saw too many startup roadshows every day. They cared about only two things: Will this thing increase my workload? And if something goes wrong, who is responsible?

At eight that evening, his left foot began to spasm. He took off his sock and pressed a hot towel over his ankle. The muscles jumped out of control, as if tiny currents of electricity were darting beneath the skin. He bit down on the towel and made no sound. Xiaoman turned over, her breathing even. The tick of the monitor and the engineering unit’s low-frequency running sound wove together. Lin Chen closed his eyes and mentally ran through tomorrow’s route: arrive at the special-needs outpatient waiting area forty minutes early; bring two paper backups; demo unit fully charged; two spare lead wires. If Director Zhao asked about data compliance, show the ethics approval and the desensitization agreement directly. No detours, no promises beyond their capabilities.

At one in the morning, his phone screen lit up. It was not Su Man, but a text message from an unfamiliar number: Mr. Lin, Director Zhao has temporarily adjusted his schedule. Wednesday morning has been changed to nine o’clock, location moved to the Neurology Department teaching room. Please bring the original data logs and the complete course-of-disease comparison table for the past three months. Also: Director Zhao says that if the device can run through the atypical-seizure cohort from his paper last year, the filing can go through the green channel.

Lin Chen stared at the screen, his finger suspended over the keyboard. Atypical-seizure cohort. That was Director Zhao’s core research direction, and the data had never been made public. This meant Wednesday’s demo was no longer a product acceptance check, but a technical defense. He slowly sat up straight, a stab of pain coming from his left foot. He opened the computer, pulled up the Municipal Second Hospital’s dataset, and began rematching the feature library. Outside the window, the wind rose again, making the glass tremble faintly. The ninety-day countdown was compressed, in this moment, into seventy-two hours. And the real threshold was not in the meeting room, but inside that stretch of waveform that had never been annotated.