Visual guidance (VG) plays an essential role in directing user attention in virtual reality (VR) and augmented reality (AR) environments. However, traditional approaches rely on explicit visual annotations, which often compromise visual clarity and increase user cognitive load. To address this issue, we propose an unobtrusive VG technique based on color vibration, a phenomenon in which rapidly alternating colors at frequencies above 25 Hz are perceived as a single intermediate color. Our work explores a perceptual state that exists between complete color fusion and visible flicker, where color differences remain detectable without conscious awareness of vibration. Through two experimental studies, we first identified the thresholds separating complete fusion, this intermediate perceptual state, and visible flicker by systematically varying color vibration parameters. Subsequently, we applied color vibrations with derived thresholds to natural image regions and validated their attention-guiding capabilities using eye-tracking measurements. The results demonstrate that controlled color vibration successfully directs user attention while maintaining low cognitive demand, providing an effective method for implementing unobtrusive VG in VR and AR systems.

We propose HaptoFloater, a low-latency mid-air visuo-haptic augmented reality (VHAR) system that utilizes imperceptible color vibrations. When adding tactile stimuli to the visual information of a mid-air image, the user should not perceive the latency between the tactile and visual information. However, conventional tactile presentation methods for mid-air images, based on camera-detected fingertip positioning, introduce latency due to image processing and communication. To mitigate this latency, we use a color vibration technique; humans cannot perceive the vibration when the display alternates between two different color stimuli at a frequency of 25 Hz or higher. In our system, we embed this imperceptible color vibration into the mid-air image formed by a micromirror array plate, and a photodiode on the fingertip device directly detects this color vibration to provide tactile stimulation. Thus, our system allows for the tactile perception of multiple patterns on a mid-air image in 59.5 ms. In addition, we evaluate the visual-haptic delay tolerance on a mid-air display using our VHAR system and a tactile actuator with a single pattern and faster response time. The results of our user study indicate a visual-haptic delay tolerance of 110.6 ms, which is considerably larger than the latency associated with systems using multiple tactile patterns.

In wireless feedback control systems, reducing packet loss is critical. The use of channel coding may decrease such packet loss; however, redundancy in channel coding also decreases the packet transmission rate although the bit rate remains the same. Thus, control systems are highly affected by disturbances. To improve control system quality, channel coding should be adaptively employed on the basis of packet loss and disturbances. Herein, an on-off error control coding scheme based on the communication and control layers is proposed. In this scheme, channel coding is adaptively used to minimize tracking errors in a controlled plant. Results demonstrate that the proposed on-off error control coding scheme improves the control system's reference tracking performance compared with that when using a fixed-rate coding scheme.

Packet loss is the major weakness of wireless feedback control systems. In this paper, we discuss the improvement of the control quality of wireless feedback control systems with Forward Error Correction (FEC) coding. If FEC coding is used, packet losses may decrease. But its redundancy decreases the packet transmission rate under the same bit rate, so that the control quality will be worse. Therefore, we propose an adaptive coding scheme to improve the control quality. In this scheme, FEC coding is used adaptively based on a predicted state of the controlled plant. Our proposal is the first approach in the field of adaptive channel coding for wireless feedback control systems because this scheme adapts channel coding to the quality of the control layer (application layer). In this paper, we show that the proposed adaptive coding scheme improves the control quality more than that of the fixed rate coding in Rayleigh fading channels.

In wireless feedback control systems, it is important how to reduce packet losses. If channel coding is used, packet losses may decrease. But its redundancy decreases the packet transmission rate under the same bit rate, so that disturbances in the controlled plant may deteriorate the quality of the control system. To improve the quality of the control system, the channel coding should be used adaptively based on packet losses and disturbances. In this paper, we propose an adaptive coding scheme based on the quality of the communication layer and the control (application) layer. In this scheme, the channel coding is used adaptively based on a predicted state of the controlled plant under a packet loss rate. We show that the proposed adaptive coding improves the control quality compared with that of the fixed rate coding.