Ultrasonic Mid-Air Haptics on the Face: Effects of Lateral Modulation Frequency and Amplitude on Users’ Responses

Title of the Paper

Ultrasonic Mid-Air Haptics on the Face: Effects of Lateral Modulation Frequency and Amplitude on Users’ Responses

Paper Information

• Subject Area: Application of ultrasonic mid-air haptics on facial regions
• Keywords: Ultrasonic mid-air haptics, facial interaction, lateral modulation, perceived intensity, emotional response, virtual reality, parameter optimization

Research Background and Issues

• What problems or challenges did the authors identify?

  • Ultrasonic mid-air haptics (UMH) is an emerging contactless, high-precision feedback technology. While significant progress has been made in studies focusing on hand-based tactile feedback, its application on the face remains a relatively underexplored research area.
  • Traditional tactile devices typically require physical contact, are bulky, and lack flexibility, making them unsuitable for practical scenarios.
  • The tactile characteristics and perception mechanisms of the face differ significantly from those of the hands, necessitating further research to support the applicability of contactless haptic feedback on facial regions.

• Why is this issue important?

  • The face, with its dense mechanoreceptors and high sensitivity, coupled with its visibility and ease of use, makes it an ideal interface for human-computer interaction.
  • UMH offers high spatial and temporal resolution tactile feedback, with potential applications in virtual reality, augmented reality, and various practical scenarios (e.g., automotive user interfaces).

• Research Motivation and Related Work:

  • The study aims to address the gap in UMH applications on the face and to explore the effects of modulation parameters (frequency and amplitude) on user perception and emotional responses.
  • Unlike existing studies that primarily focus on the hands or specific parameters (e.g., AM modulation on facial regions), this research covers a broader range of parameters across different facial areas.
  • The goal is to establish design guidelines to inform future system development.

Solutions

• What methods or solutions did the authors propose?

  • The study employs lateral modulation (LM) technology to investigate UMH's tactile perception and emotional impact on different facial areas (lips, nose tip, and cheeks).
  • Two key LM parameters were adjusted: frequency (10Hz, 40Hz, 70Hz, and 100Hz) and amplitude (3mm, 6mm, 9mm, and 12mm). The effects of each combination on perceived intensity, valence (pleasantness), and arousal were systematically tested.

• What are the innovative aspects of this solution?

  • Compared to traditional contact-based tactile methods or studies focused solely on the hands, this research is the first to explore the combined effects of UMH parameter adjustments on multisensory and emotional responses from a facial perspective.
  • By comparing the differences in mechanoreceptors between the hands and face (e.g., glabrous skin on the lips vs. hairy skin on the nose tip and cheeks), the study optimizes parameter selection for specific facial regions.

• Implementation Steps and Key Technologies:

  1. The experiment consisted of three phases:
     • Training Phase: Participants familiarized themselves with the experimental equipment, tactile sensations, and rating methods.
     • Data Collection Phase: Sixteen LM stimuli were repeatedly applied to three facial regions (lips, nose tip, and cheeks), and participants provided subjective ratings on perceived intensity, valence, and arousal.
     • Data Analysis Phase: Repeated measures ANOVA was used to statistically analyze the effects of different parameter combinations.
  2. Experimental equipment included a UMH device (STRATOS Explore), a depth camera (for precise facial position tracking), and a head stabilization apparatus.
  3. Perceived intensity was rated using the Absolute Magnitude Estimation (AME) method, while valence and arousal were quantified using the Self-Assessment Manikin (SAM) scale.

Research Outcomes

• What specific results were achieved?

  1. Different facial regions exhibited significant differences in tactile perception and emotional responses to UMH:
     • The lips showed significantly higher perceived intensity than the nose tip and cheeks, indicating greater sensitivity of glabrous skin.
     • Feedback on the nose tip elicited calmer responses (lower arousal), while the lips induced more excitement.
  2. The effects of LM parameters on tactile and emotional responses:
     • Larger LM amplitudes resulted in higher tactile intensity and arousal. The optimal amplitude range was identified as 9mm-12mm.
     • Optimal frequencies varied across facial regions: 70Hz for the lips and 40Hz for the nose tip and cheeks.
  3. No significant effect of UMH parameters on emotional valence (pleasantness) was observed.

• What advantages does it have over existing solutions?

  • The study proposed UMH-based facial tactile design guidelines based on parameter modulation, which can be extended to various interaction scenarios.
  • It expanded the scope of UMH research, addressing the theoretical gap in parameter optimization from hand-based to facial applications.

• What were the experimental or evaluation results?

  • 72% of the experimental combinations triggered perceivable UMH feedback.
  • On the lips, LM parameter adjustments significantly enhanced intensity and emotional responses.
  • Frequencies below 40Hz failed to significantly activate tactile perception on the nose tip and cheeks.

• Limitations and Future Directions

  • Limitations:
    1. The size and real-time capabilities of the depth camera used for data collection remain insufficient for portable device requirements.
    2. The long-term safety of exposure to ultrasonic vibrations requires further validation.
    3. The current experiment relied on small-sample subjective ratings, lacking objective verification through physiological indicators.
  • Future Directions:
    1. Develop more compact and energy-efficient UMH devices and facial tracking technologies.
    2. Integrate physiological signal measurements such as EEG and heart rate to enhance research reliability.
    3. Further explore fine-grained mappings between UMH parameters and emotional effects to provide specific application strategies for fields like gaming and virtual reality.

Conclusion

This study systematically analyzed the potential of ultrasonic mid-air haptics for facial applications, particularly the effects of different frequency and amplitude parameters on tactile perception and emotional responses. The identified optimal parameters and design recommendations lay a theoretical foundation for optimizing future contactless human-computer interaction systems and suggest potential application scenarios in autonomous driving, inclusive design, and immersive virtual reality.