Dozer: Toward Understanding the Design of Closed-Loop Wearables for Sleep

Title of the Paper

Dozer: Towards understanding the design of closed-loop wearables for sleep

Paper Information

• Subject Area: Sleep health technology and closed-loop wearable device design
• Keywords: Brain-computer interface, closed-loop, EEG, transcranial alternating current stimulation (tACS), sleep, neuromodulation, wearable devices

Research Background and Problem Statement

• Identified Problems or Challenges:

  • Sleep is crucial for cognitive function, mental health, and physical well-being, yet sleep-related issues are increasingly prevalent worldwide.
  • Current sleep technologies primarily focus on sleep tracking, while the design of technologies that actively promote sleep remains underexplored.
  • Users often face challenges such as difficulty interpreting data provided by devices or lack of adherence to device usage.

• Significance:

  • Improving sleep can help address various health issues such as depression and insomnia, enhancing overall quality of life.
  • Properly designed closed-loop systems that integrate neuromodulation with real-time sleep state monitoring could provide novel solutions for sleep issues outside clinical settings.

• Research Motivation and Related Work:

  • Previous studies have shown that neuromodulation methods (e.g., transcranial electrical stimulation) and auditory stimulation (e.g., pink noise) can help regulate sleep.
  • While some laboratory-based neuromodulation technologies have demonstrated potential, integrating these technologies into wearable devices for everyday use remains insufficiently explored.
  • The authors propose leveraging EEG sensing and neuromodulation technologies to investigate the potential of closed-loop wearable devices.

Solution

• Proposed Method or Solution:

  • Designed a closed-loop wearable system called "Dozer," whose core functionality involves detecting user drowsiness based on EEG data and accelerating sleep onset through transcranial alternating current stimulation (tACS) and pink noise stimulation.
  • The system is presented as a hat embedded with relevant hardware (e.g., EEG sensors, electrical stimulation modules, and speakers) for users to wear while sleeping.

• Innovations:

  • Integration of sleep state detection with sleep-promoting technologies (electrical stimulation and auditory modulation) into a single closed-loop system.
  • Enables use in non-laboratory environments, allowing continuous monitoring and influence on natural sleep processes.
  • Introduces a design framework that integrates human physiology with technological interaction.

• Implementation Steps and Key Technologies:

  1. EEG Data Collection and Analysis:
     • Real-time monitoring of brain activity using seven scalp EEG electrodes.
     • Detection of user drowsiness through analysis of the Theta/Alpha ratio.
  2. Automatic Stimulation Triggering:
     • Initiates tACS (0.65mA, 5Hz) and synchronized pink noise stimulation upon detecting drowsiness.
  3. Hardware Design:
     • All electronic components are integrated into a double-layered hat to ensure portability and comfort.
  4. User Participation and Testing:
     • Conducted 24-hour tests in real-life scenarios with 11 participants.

Research Outcomes

• Specific Findings:

  • User feedback revealed three experiential themes:
    • Autonomy of Closed-Loop Neuromodulation: Users generally perceived the system's responsiveness to their physiological states, though some struggled to clearly sense the closed-loop process.
    • Hardware Presence: Due to discomfort in design (e.g., electrode sensation and device weight), users were aware of the device during sleep.
    • Feedback Perception: Insufficient system feedback on its operation affected users' trust and relaxation while using the device.
  • Users reported falling asleep despite device-related issues rather than because of its functionality.

• Advantages Compared to Existing Solutions:

  • Successfully demonstrated the feasibility of closed-loop wearable technology, combining EEG detection and neuromodulation to enhance personalized sleep potential.
  • Emphasized transparency and user perception of functionality, improving applicability from a technology-psychology integration perspective.

• Experimental Results:

  • While some participants perceived certain effects from electrical and auditory stimulation, the device's low comfort level and inadequate feedback mechanisms limited its actual sleep-promoting effectiveness.
  • The study further validated the critical impact of hardware design, user feedback, and closed-loop design on user experience.

• Limitations and Future Directions:

  • Limitations:
    • Short study duration prevented comprehensive observation of long-term usage potential and limitations.
    • Significant hardware comfort issues negatively influenced experience and effectiveness.
  • Future Directions:
    • Enhance device comfort by using softer electrode materials and adjusting electrode placement.
    • Introduce customizable feedback features to help users better understand device operation.
    • Combine laboratory and field studies for more systematic effectiveness evaluation.
    • Improve physical design to minimize interference with users' sleeping posture and comfort.

Conclusion

This paper presents the design and preliminary validation of a closed-loop wearable device based on EEG and neuromodulation, highlighting potential areas for improvement. It offers valuable design strategies and insights for advancing sleep technology and optimizing user experience in future developments.