A Psychophysical Comparison of Vibrotactile and Electrotactile Feedback for Hazard Proximity Alerts

Abstract

In visually and auditory demanding construction environments, haptic feedback offers a promising alternative for delivering hazard proximity alerts. This study presents a preliminary psychophysical comparison of vibrotactile and electrotactile feedback to evaluate their suitability for multitasking scenarios involving vehicle operation. Using a simulated excavation task with environmental noise, absolute and difference thresholds were measured via the method of limits. Results from five participants showed that vibrotactile feedback had a lower and more consistent sensation threshold (9.3%) than electrotactile feedback (19.9%) and greater sensitivity to intensity changes (Weber Fraction = .13 vs. .20). Electrotactile feedback exhibited higher perceptual variability and signs of adaptation. These findings suggest vibrotactile feedback may be more effective for time-sensitive alerts, while electrotactile systems may require calibration. This foundational work supports the design of haptic interfaces to improve situational awareness and safety in high-risk, multisensory construction settings. Future work will expand testing in immersive virtual environments.

Introduction

In high-risk environments like construction, spatial awareness is critical for safety and efficiency. However, supporting it is difficult due to limited visual and auditory bandwidth caused by vehicle operation and environmental noise, highlighting the need for alternative feedback modalities in multitasking settings (Hossain et al., 2023). Haptic feedback, specifically vibrotactile and electrotactile, offers a nonvisual and nonauditory means of conveying critical information. Vibrotactile cues, delivered via mechanical vibrations, have been widely used in balance rehabilitation and hazard awareness (Lim & Yang, 2023; Lind et al., 2020), and have shown promise in enhancing spatial awareness during navigation tasks (Hossain et al., 2025). However, machine-induced vibration in construction may reduce their effectiveness. Electrotactile feedback, which stimulates sensory nerves electrically, may be less affected by masking and offer more precise signaling (Dideriksen et al., 2022). While both modalities can convey spatial cues, their relative performance in multitasking construction settings remains unclear. This study presents a preliminary psychophysical investigation comparing absolute and difference thresholds for both modalities, offering foundational insight into their feasibility for vehicle navigation and environmental scanning in complex work environments.

Background

Excavation operations pose significant safety risks due to frequent interactions with underground hazards (U.S. Bureau of Labor Statistics, 2021). Visual indicators such as signage and flaggers are commonly used to provide hazard warnings, but they depend on workers noticing them at the right moment. In visually and auditorily demanding environments, such alerts may go unnoticed (Marks & Teizer, 2013). Haptic feedback offers a promising alternative by delivering tactile alerts without relying on visual or auditory channels, which are already occupied by other task demands. According to Wickens’ (2008) Multiple Resource Theory, distributing information across separate sensory channels can improve processing efficiency. Vibrotactile feedback has been shown to enhance spatial awareness with minimal added cognitive load (Márquez-Sánchez et al., 2021). Electrotactile feedback, which stimulates sensory nerves via mild electric current, may offer more sensitive cues, but its suitability in multitasking settings such as construction remains unclear. This study explores perception thresholds and resolution for both modalities to inform the design of haptic interfaces that support situational awareness in construction safety contexts.

Approach

A psychophysical comparison study was conducted to determine absolute and difference thresholds for electrotactile and vibrotactile feedback using the method of limits. To simulate the sensory demands of construction environments, participants operated a virtual construction vehicle while listening to construction site noise through noise canceling headphones. Vibrotactile feedback was delivered using a haptic motor embedded in a Logitech Extreme 3D Pro joystick, while electrotactile stimuli were provided by a TENS unit with electrode pads placed at corresponding hand locations. For absolute threshold detection, stimulus intensity was gradually increased from a low level until participants reported perception, then decreased until perception ceased. Thresholds were calculated as the average transition point across ten trials. For difference thresholds, base stimuli were set just above the absolute threshold, followed by comparison stimuli with slightly higher or lower intensity. All stimuli remained above the perception threshold. Participants judged whether a difference was detected; the smallest reliably detected change 50% of the time was recorded as the difference threshold.

Outcome

All participants successfully completed the spatial task, indicating no tradeoff in performance and allowing focus on the psychophysical comparison. Preliminary analysis of five participants showed a sensation threshold of 9.3% intensity for vibrotactile feedback and 19.9% for electrotactile feedback. Electrotactile thresholds displayed greater variability across participants, as shown in Figure 1. During descending trials, electrotactile thresholds were higher, suggesting adaptation over time. Vibrotactile thresholds were more consistent between ascending and descending trials and had a lower overall sensation threshold.

Figure 1.

Mean sensory thresholds for ascending and descending trials in vibrotactile and electrotactile stimulation.

For vibrotactile feedback, with a base intensity of 10%, participants detected a change at 1.3%, yielding a Weber Fraction of .13. For electrotactile feedback, with a base intensity of 25%, the change was detected at 5%, resulting in a Weber Fraction of .20. The higher Weber Fraction for electrotactile feedback suggests reduced sensitivity to intensity changes.

These findings provide insight into haptic perception under competing sensory demands. The lower threshold and higher consistency of vibrotactile feedback suggest it may allow faster detection, making it more suitable for time critical alerts. This aligns with previous findings of lower Weber fractions on the palm due to higher receptor density (Mountcastle, 2005; Weinstein, 1968). In contrast, electrotactile feedback showed more individual variability and signs of sensory adaptation. The increased threshold during descending trials suggests reduced sensitivity with prolonged exposure (Kourtesis et al., 2022). These findings suggest that electrotactile feedback may require adjustable intensity settings or periodic recalibration to maintain effectiveness over prolonged use.

Conclusion

This preliminary study identified baseline thresholds for vibrotactile and electrotactile feedback, offering early guidance for designing haptic interfaces for hazard alerts. Vibrotactile feedback produced more consistent responses, while electrotactile feedback, though potentially less affected by whole body vibration, showed greater variability and signs of adaptation. These results highlight the importance of choosing suitable feedback modalities in environments with competing sensory demands. Limitations include the small sample size and simulated setting. Future research will expand into a virtual excavation scenario to examine impacts on performance, awareness, and workload in realistic conditions.