Visual Warning Signals Research Articles

Enhancing Safety in Autonomous Vehicles: The Impact of Auditory and Visual Warning Signals on Driver Behavior and Situational Awareness

Semi-autonomous vehicles (AVs) enable drivers to engage in non-driving tasks but require them to be ready to take control during critical situations. This “out-of-the-loop” problem demands a quick transition to active information processing, raising safety concerns and anxiety. Multimodal signals in AVs aim to deliver take-over requests and facilitate driver–vehicle cooperation. However, the effectiveness of auditory, visual, or combined signals in improving situational awareness and reaction time for safe maneuvering remains unclear. This study investigates how signal modalities affect drivers’ behavior using virtual reality (VR). We measured drivers’ reaction times from signal onset to take-over response and gaze dwell time for situational awareness across twelve critical events. Furthermore, we assessed self-reported anxiety and trust levels using the Autonomous Vehicle Acceptance Model questionnaire. The results showed that visual signals significantly reduced reaction times, whereas auditory signals did not. Additionally, any warning signal, together with seeing driving hazards, increased successful maneuvering. The analysis of gaze dwell time on driving hazards revealed that audio and visual signals improved situational awareness. Lastly, warning signals reduced anxiety and increased trust. These results highlight the distinct effectiveness of signal modalities in improving driver reaction times, situational awareness, and perceived safety, mitigating the “out-of-the-loop” problem and fostering human–vehicle cooperation.

A self-healing and recyclable polyurethane composite film for durable pH responsive coating

Wearable pH sensors can offer a visual warning signal of pH changes, making them particularly attractive in health monitoring and environmental detection. However, the fabrication of durable wearable pH sensors remains challenging due to the inevitable damage that sensors suffer in practical applications. Here, a durable pH responsive coating fabric with outstanding self-healing and recyclable capabilities is prepared with a composite film composed of a dynamic boroxine-polyurethane (BPU) and a pH responsive Congo red-based polymeric dye (CRPD). The BPU/CRPD composite film exhibits a high tensile strength of 17.46 MPa, breaking elongation of 407 %, toughness of 31.61 MJ/m3, Young’s modulus of 11.78 MPa, and outstanding elastic restorability. The high reversibility of boroxines and hydrogen bonds enable the composite film with healing efficiency of 87 % at 70 °C for 2 h and recycling efficiency of 97 % under 3 MPa at 80 °C for 5 min. In addition, the BPU/CRPD coated fabric presents outstanding pH responsive property and color fastness. Importantly, the scratched coating fabric can be easily healed at 70 °C, 5 MPa for 5 min or using an electric iron. Furthermore, the BPU/CRPD coatings on the discarded fabric can be recycled and reused many times with similar pH responsive behavior. The outstanding fastness, self-healing and recycling properties promote the durability of the pH responsive coating. This work provides a meaningful strategy for developing durable pH responsive coating fabrics with self-healing and recycling capabilities that will be promising for wearable pH sensors.

Evaluation of spatio-temporal electrocutaneous warning signals

Abstract Acoustic or visual warning signals for workers in hazardous situations might fail under loud and/or lowvisibility work situations. A warning system that uses electrocutaneous stimulation can overcome this problem. The aim of this pilot study was to find spatio-temporal stimulation patterns for appropriate electrical warning. Eight electrode pairs were attached to the upper right arm of 16 participants. The stimulation was conducted with bi-phasic rectangular pulses of 150 μs and an amplitude of up to 25 mA. Pulse intervals that generate a single pulse, pulsating, vibrating, and continuous perception as well as varying spatial patterns (e.g. alternating between electrode pairs or circumferentially around the arm) were investigated and evaluated with regard to alertness, discomfort, and urgency. The pilot study revealed that a stimulation signal that generates a vibrating perception and is applied as a circumferential signal around the arm showed the highest values of alertness and is therefore considered a potential warning pattern for future studies with larger study groups.

Driver's attitudes and preferences toward connected vehicle information system

Connected vehicle (CV) and vehicle-to-everything (V2X) technologies enhance connectivity among vehicle, road user, and road infrastructure and can provide timely and concisely coordination information among drivers. Currently, there are far more studies on the technical aspects of V2X than on the demands of users. This study investigated the attitudes and preferences of drivers concerning the design of connected vehicle information system (CVIS) in this context. Focus group discussions followed by a questionnaire survey were conducted to gather driver's attitudes and preferences information. Results indicate that participants believed CVISs would help improve the efficiency of roadway communication, thereby improving safety, efficiency, and convenience of the overall traffic system. Visual warning signals and descriptive verbal speech were preferred over tactile warnings. Safety-related information (e.g., rescue services, reminding vehicle malfunction, and information about surroundings hazards) was valued most. Furthermore, age, gender, risk perception, privacy expectations, and technology inclination played essential roles in associating the attitudes toward CVISs. The outcome of this research provides an overview of the opinion of Chinese drivers toward CVISs and suggests practical implications regarding the design of CVISs for intelligent transportation.

White bark in birch species as a warning signal for bark-stripping mammals

Background : Birch species such as Betula pendula have conspicuous white bark and the evolutionary drivers for this colouration remain unresolved. Aims We evaluated our hypothesis that the white bark is a visual warning signal to deter mammals from bark-stripping. Many species of deer (Cervidae) and multiple other mammals consume bark. White birch species’ bark contains betulin and other compounds which likely make the bark unprofitable for herbivores. The white bark has features consistent with a visual signal for mammalian herbivores and could act as a visual aposematic signal of chemical defence. Methods We compared deer bark-stripping between tree species in Scottish woodlands. For Betula pendula, we compared stripping of juvenile brown bark with mature white bark. We also reviewed existing literature to find the tree-species preference for a wide-range of bark-stripping mammals. Results In Scotland, we found that white-barked birch bark was less preferred. We also found mature white birch bark was avoided compared to juvenile brown bark. Existing literature for multiple herbivores showed that white birch species’ bark was often either not preferred or avoided. Conclusion We suggest that the conspicuous white colouration of birch bark may act as an aposematic visual signal to deter bark-stripping mammals.

Effects of Temporal Characteristics on Pilots Perceiving Audiovisual Warning Signals Under Different Perceptual Loads.

Our research aimed to investigate the effectiveness of auditory, visual, and audiovisual warning signals for capturing the attention of the pilot, and how stimulus onset asynchronies (SOA) in audiovisual stimuli affect pilots perceiving the bimodal warning signals under different perceptual load conditions. In experiment 1 of the low perceptual load condition, participants discriminated the location (right vs. left) of visual targets preceded by five different types of warning signals. In experiment 2 of high perceptual load, participants completed the location task identical to a low load condition and a digit detection task in a rapid serial visual presentation (RSVP) stream. The main effect of warning signals in two experiments showed that visual and auditory cues presented simultaneously (AV) could effectively and efficiently arouse the attention of the pilots in high and low load conditions. Specifically, auditory (A), AV, and visual preceding auditory stimulus by 100 ms (VA100) increased the spatial orientation to a valid position in low load conditions. With the increase in visual perceptual load, auditory preceding the visual stimulus by 100 ms (AV100) and A warning signals had stronger spatial orientation. The results are expected to theoretically support the optimization design of the cockpit display interface, contributing to immediate flight crew awareness.

Audio-Vision Emergency Vehicle Detection

Emergency vehicles (EVs) are permitted to travel at high speed to quickly reach the destination with the aid of audible and visual warning signals, and other road users are required to clear the path for EVs. However, car drivers may sometimes be unaware of nearby EVs, leading to delay in response or even traffic collisions. This work proposes audio-based and vision-based EV detection systems (EVD) that can detect EVs and alert car drivers to respond appropriately. First, we propose a modified YOLO model tailored to the EVD problem, namely YOLO-EVD, and develop a novel image dataset for vision-based EVD (V-EVD). We utilize cross-stage partial connections at the YOLO-EVD’s neck to enhance the detection performance, in which YOLO-EVD achieves 95.5% mean average precision that is better than those of the other single-stage object detectors. Second, we propose WaveResNet, an end-to-end convolutional neural network, for audio-based EVD (A-EVD) based on the classification of siren sound and traffic noise. With raw waveform input of at least one second, the WaveResNet attains high accuracies, at above 98% in normal traffic, and is robust to noise. Both YOLO-EVD and WaveResNet meet the real-time operation requirement. Also, we integrate YOLO-EVD and WaveResNet to develop a prototype of the audio-vision EVD system (AV-EVD) that is a novel approach in the literature of the EVD problem. Our experiments show the promising results of the AV-EVD system as it produces a low misdetection rate of 1.54%. The proposed A-EVD, V-EVD, and AV-EVD systems can be applied to provide safety functions for private cars, self-driving cars, or smart road infrastructure.

Multimodal Aposematic Defenses Through the Predation Sequence

Aposematic organisms warn predators of their unprofitability using a combination of defenses, including visual warning signals, startling sounds, noxious odors, or aversive tastes. Using multiple lines of defense can help prey avoid predators by stimulating multiple senses and/or by acting at different stages of predation. We tested the efficacy of three lines of defense (color, smell, taste) during the predation sequence of aposematic wood tiger moths (Arctia plantaginis) using blue tit (Cyanistes caeruleus) predators. Moths with two hindwing phenotypes (genotypes: WW/Wy = white, yy = yellow) were manipulated to have defense fluid with aversive smell (methoxypyrazines), body tissues with aversive taste (pyrrolizidine alkaloids) or both. In early predation stages, moth color and smell had additive effects on bird approach latency and dropping the prey, with the strongest effect for moths of the white morph with defense fluids. Pyrrolizidine alkaloid sequestration was detrimental in early attack stages, suggesting a trade-off between pyrrolizidine alkaloid sequestration and investment in other defenses. In addition, pyrrolizidine alkaloid taste alone did not deter bird predators. Birds could only effectively discriminate toxic moths from non-toxic moths when neck fluids containing methoxypyrazines were present, at which point they abandoned attack at the consumption stage. As a result, moths of the white morph with an aversive methoxypyrazine smell and moths in the treatment with both chemical defenses had the greatest chance of survival. We suggest that methoxypyrazines act as context setting signals for warning colors and as attention alerting or “go-slow” signals for distasteful toxins, thereby mediating the relationship between warning signal and toxicity. Furthermore, we found that moths that were heterozygous for hindwing coloration had more effective defense fluids compared to other genotypes in terms of delaying approach and reducing the latency to drop the moth, suggesting a genetic link between coloration and defense that could help to explain the color polymorphism. Conclusively, these results indicate that color, smell, and taste constitute a multimodal warning signal that impedes predator attack and improves prey survival. This work highlights the importance of understanding the separate roles of color, smell and taste through the predation sequence and also within-species variation in chemical defenses.

Safety Helmets for Motorcycle Rider with Hearing Impairment

Motorcycle fatal accidents on roads in Malaysia are one of the major causes of death and injuries. There is a need to increase and improvise road safety awareness. In Malaysia, riders with hearing impairment are allowed to ride a motorcycle on the road but restrictions such as responding to the surrounding sounds, especially the sounds produced by the horns and emergency siren from other vehicles warrant a high degree of concern. In this work, a safety helmet is designed to aid the rider with hearing impairment, in detecting the sounds produced by the horns and emergency siren of vehicles. A simple mechanism is developed by using sound sensors as the input, light-emitting diode (LEDs) as the output, and Arduino Uno Board as the controller. The threshold of the sound sensor is 96 dB. When the sensor detected sound waves that exceed the threshold, the LEDs will turn on, which serves as the awareness indication for the rider with hearing impairment. The functionality of the sound detection mechanism in the designed safety helmet is tested based on its response to car and motorcycle horns. The sound intensity produced by car and motorcycle horns is in the range of 107 – 109 dB and 96 – 105 dB. Respectively. The functionality test was conducted at three different distances starting from 4.7m, 9.4m, and 14.10m and the developed system operates to detect the sound of horns in the range of 120-90 dB. Finite element analysis was also performed in analyzing the carbon fiber material for the designed safety helmet, which shows the least deformation (6.174 mm) with the stress of 1014 MPa resulting in the lowest strain of 0.01181 when the load of 3432N was applied to it vertically. Safety helmets that impair hearing with hearing aids are crucial for riders with hearing impairment. However, this work implements an alternative method that focused on using visual warning signals instead of audible warning signals, in aiding the riders with hearing impairment, especially completely deaf riders to stay alert and safe on the road.

Sensation thresholds in electrocutaneous stimulation

Abstract Acoustic or visual warning signals for workers in hazardous situations might fail under loud and/or lowvisibility work situations. A warning system should be developed that uses electrocutaneous stimulation through textile electrodes. Previous work investigated suitable stimulation parameters using TENS electrodes. The aim of this study was to compare TENS and textile cuff electrodes in terms of sensation thresholds, qualitative and spatial sensation. A study on 30 healthy volunteers (f=13, m=17) of mean age of 26.7 years was conducted applying bi-phasic rectangular current pulses to electrodes attached to the upper right arm. The study revealed that perception, attention and intolerance thresholds, qualitative and spatial perception are comparable indicating that future studies with the textile cuff electrodes can be generally based on the previous results with TENS electrodes.

Attacks by predators on artificial cryptic and aposematic insect larvae

AbstractColour and colour patterns seem to be especially important visual warning signals for predators, which might have innate or learned ability to avoid aposematic prey. To test the importance of larval colour pattern of the aposematic ladybird Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), an invasive alien species in Europe, we presented the plasticine models of aposematic larvae to wild and naïve birds. We studied the attacks on aposematic larvae of various patterns and colours in nature and in an outdoor aviary. The larvae were cryptic (green), aposematic (resembling those of the H. axyridis larvae), and semi‐aposematic (i.e., black but missing the typical orange patches of H. axyridis larvae). We detected attacks on 71 larvae out of 450 (i.e., 2.6% daily predation). Twenty‐nine attacks were made by birds, 37 by arthropods, and five by gastropods. Wild birds attacked green and black larvae significantly more often than aposematic larvae. Colour did not have an effect on attacks by arthropods. The experiment with naïve birds was conducted in an outdoor aviary, where naïve great tits, Parus major L., were offered the same artificial larvae as in the first experiment. In total, 57 of 90 exposed larvae were attacked by birds (i.e., 28% daily predation), and green larvae were attacked significantly more than the aposematic larvae (but not more than black larvae). Our results imply that aposematic larvae of H. axyridis are more than 12× less likely to be predated by birds than green larvae in nature. The aposematic pattern represented a more effective signal than the semi‐aposematic signal. The ability to reject aposematic prey seemed to be innate in our birds.

The effectiveness of livestock protection measures against wolves (Canis lupus) and implications for their co-existence with humans

Wolves (Canis lupus) can kill domestic livestock resulting in intense conflicts with humans. Damage to livestock should be reduced to facilitate human-wolf coexistence and ensure positive outcomes of conservation efforts. Current knowledge on the effectiveness of livestock protection measures from wolves is limited and scattered in the literature. In this study, we compiled a dataset of 30 cases describing the application of 11 measures of protecting cattle and smaller livestock against wolves, estimated their effectiveness as a relative risk of damage, and identified the best measures for damage reduction. We found that: (1) lethal control and translocation were less effective than other measures, (2) deterrents, especially fladry which is a fence with ropes marked by hanging colored flags that sway in the wind and provide a visual warning signal, were more effective than guarding dogs; (3) deterrents, fencing, calving control and herding were very effective, but the last two measures included only one case each; and (4) protection of cattle was more effective than that of small stock (sheep and goats, or sheep only) and mixed cattle and small stock. In all of these cases, the relative risk of damage was reduced by 50–100%. Considering Germany as an example of a country with a recovering wolf population and escalating human-wolf conflicts, we suggest electric fences and electrified fladry as the most promising measures, which under suitable conditions can be accompanied by well-trained livestock guarding dogs, and the temporary use of deterrents during critical periods such as calving and lambing seasons. Further research in this field is of paramount importance to efficiently mitigate human-wolf conflicts.

No evidence of quantitative signal honesty across species of aposematic burnet moths (Lepidoptera: Zygaenidae).

Many defended species use conspicuous visual warning signals to deter potential predators from attacking. Traditional theory holds that these signals should converge on similar forms, yet variation in visual traits and the levels of defensive chemicals is common, both within and between species. It is currently unclear how the strength of signals and potency of defences might be related: conflicting theories suggest that aposematic signals should be quantitatively honest, or, in contrast, that investment in one component should be prioritized over the other, while empirical tests have yielded contrasting results. Here, we advance this debate by examining the relationship between defensive chemicals and signal properties in a family of aposematic Lepidoptera, accounting for phylogenetic relationships and quantifying coloration from the perspective of relevant predators. We test for correlations between toxin levels and measures of wing colour across 14 species of day‐flying burnet and forester moths (Lepidoptera: Zygaenidae), protected by highly aversive cyanogenic glucosides, and find no clear evidence of quantitative signal honesty. Significant relationships between toxin levels and coloration vary between sexes and sampling years, and several trends run contrary to expectations for signal honesty. Although toxin concentration is positively correlated with increasing luminance contrast in forewing pattern in 1 year, higher toxin levels are also associated with paler and less chromatically salient markings, at least in females, in another year. Our study also serves to highlight important factors, including sex‐specific trends and seasonal variation, that should be accounted for in future work on signal honesty in aposematic species.

Effects of bright light treatment on psychomotor speed in athletes.

Purpose: A recent study suggests that transcranial brain targeted light treatment via ear canals may have physiological effects on brain function studied by functional magnetic resonance imaging (fMRI) techniques in humans. We tested the hypothesis that bright light treatment could improve psychomotor speed in professional ice hockey players.Methods: Psychomotor speed tests with audio and visual warning signals were administered to a Finnish National Ice Hockey League team before and after 24 days of transcranial bright light or sham treatment. The treatments were given during seasonal darkness in the Oulu region (latitude 65 degrees north) when the strain on the players was also very high (10 matches during 24 days). A daily 12-min dose of bright light or sham (n = 11 for both) treatment was given every morning between 8 and 12 am at home with a transcranial bright light device. Mean reaction time and motor time were analyzed separately for both psychomotor tests. Analysis of variance for repeated measures adjusted for age was performed.Results: Time × group interaction for motor time with a visual warning signal was p = 0.024 after adjustment for age. In Bonferroni post-hoc analysis, motor time with a visual warning signal decreased in the bright light treatment group from 127 ± 43 to 94 ± 26 ms (p = 0.024) but did not change significantly in the sham group 121 ± 23 vs. 110 ± 32 ms (p = 0.308). Reaction time with a visual signal did not change in either group. Reaction or motor time with an audio warning signal did not change in either the treatment or sham group.Conclusion: Psychomotor speed, particularly motor time with a visual warning signal, improves after transcranial bright light treatment in professional ice-hockey players during the competition season in the dark time of the year.

How to present collision warnings at intersections?—A comparison of different approaches

Analyses of intersection accidents have shown that in most cases drivers overlook or see other road users with the right of way too late that they cannot react in time. Appropriate visual warning signals which support drivers in their attention allocation and driving behavior could be useful to improve drivers’ reaction. In a driving simulator study, two warning strategies varying in their timing: (1) top-down warning while approaching a critical intersection and (2) bottom-up warning directly before the critical incident were investigated in a T-intersection situation. For the bottom-up warning, two warning signal designs were compared. 48 subjects (M=27.3 years, SD=7.4 years) participated in the study. Driving data as well as subjective evaluation of the three warning signals (one early and two late warning signals) were analyzed. The early warning signal which was given while approaching the intersection showed a positive effect. Here, most collisions could be avoided due to drivers’ adaptation of their driving behavior toward safer driving. They waited longer at the intersection before turning and finally turned with a lower velocity. In addition, drivers evaluated the early warning signal as very “useful”. With regard to the late warnings a much smaller effect was found. From these results, requirements can be derived for the design of effective warning strategies when driving at critical intersections.

Iridescent blue and orange components contribute to the recognition of a multicomponent warning signal

Warning colouration functions to deter predators from attacking unprofitable (e.g., unpalatable or toxic) prey items. While warning colours are often characterized by long-wavelength components (e.g., orange, red or yellow), many distasteful animals across the animal kingdom display orange or red colour patches adjacent to or within a field of short-wavelength colouration such as blue (e.g., strawberry poison dart frogs, pipevine swallowtail and pyjama nudibranch), which yields a multicomponent visual warning signal. Here we show that, in such signals, blue and orange patches can function as redundant signal components; avian predators trained not to attack the intact blue and orange colouration of the pipevine swallowtail (Battus philenor) recognised the butterflies as distasteful even when the blue and orange were presented individually. Our results demonstrate that blue colouration and potential multiple, unimodal, signal components should be considered in research on visual warning signals, including in well-studied animals, such as dendrobatid frogs and swallowtail butterflies.

Hybrid and electric low-noise cars cause an increase in traffic accidents involving vulnerable road users in urban areas

Due to resource scarcity, the number of low-noise and electric cars is expected to increase rapidly. The frequent use of these cars will lead to a significant reduction of traffic related noise and pollution. On the other hand, due to the adaption and conditioning of vulnerable road users the number of traffic accidents involving pedestrians and bicyclists is postulated to increase as well. Children, older people with reduced eyesight and the blind are especially reliant on a combination of acoustic and visual warning signals with approaching or accelerating vehicles. This is even more evident in urban areas where the engine sound is the dominating sound up to 30 kph (kilometres per hour). Above this, tyre–road interaction is the main cause of traffic noise. With the missing typical engine sound a new sound design is necessary to prevent traffic accidents in urban areas. Drivers should not be able to switch the sound generator off.

Variation in predator species abundance can cause variable selection pressure on warning signaling prey

Predation pressure is expected to drive visual warning signals to evolve toward conspicuousness. However, coloration of defended species varies tremendously and can at certain instances be considered as more camouflaged rather than conspicuous. Recent theoretical studies suggest that the variation in signal conspicuousness can be caused by variation (within or between species) in predators' willingness to attack defended prey or by the broadness of the predators' signal generalization. If some of the predator species are capable of coping with the secondary defenses of their prey, selection can favor reduced prey signal conspicuousness via reduced detectability or recognition. In this study, we combine data collected during three large-scale field experiments to assess whether variation in avian predator species (red kite, black kite, common buzzard, short-toed eagle, and booted eagle) affects the predation pressure on warningly and non-warningly colored artificial snakes. Predation pressure varied among locations and interestingly, if common buzzards were abundant, there were disadvantages to snakes possessing warning signaling. Our results indicate that predator community can have important consequences on the evolution of warning signals. Predators that ignore the warning signal and defense can be the key for the maintenance of variation in warning signal architecture and maintenance of inconspicuous signaling.

Sound affects the speed of visual processing.

The authors examined the effects of a task-irrelevant sound on visual processing. Participants were presented with revolving clocks at or around central fixation and reported the hand position of a target clock at the time an exogenous cue (1 clock turning red) or an endogenous cue (a line pointing toward 1 of the clocks) was presented. A spatially irrelevant sound presented 100 ms before the cue speeded visual latency when compared with a sound presented 100 ms after the cue. The effect of the sound was larger the farther the target was from fixation, and it was larger for endogenous than exogenous cues. A visual temporal warning signal had different effects on perceptual latency. These results demonstrate that an asynchronous sound can shift the perceived time of occurrence of a visual cue (temporal ventriloquism) and speed the velocity of the attentional shift toward the target. Sounds thus have multiple effects on visual perception.

Using Peripersonal Warning Signals to Orient a Driver’s Gaze

We report a series of three experiments designed to assess the relative speed with which people can initiate speeded head-orienting responses following the presentation of spatial warning signals. Recent cognitive neuroscience findings have shown that the human brain tends to treat stimuli occurring in peripersonal space as being somehow more behaviorally relevant and attention demanding than stimuli occurring in extrapersonal space. These brain mechanisms may be exploited in the design of warning signals. Experiment 1 assessed the effectiveness of various different unisensory warning signals in eliciting a head-turning response to look at the potential source of danger requiring participants' immediate attention; Experiment 2 assessed the latency of a driver's responses to events occurring in the cued direction; Experiment 3 assessed the relative effectiveness of various warning signals in reorienting a person's gaze back to a central driving task while he or she was distracted by a secondary task. The results show that participants initiated head-turning movements and made speeded discrimination or braking responses significantly more rapidly following the presentation of a close rear auditory warning signal than following the presentation of either a far frontal auditory warning signal, a vibrotactile warning signal presented to their waist, or a peripheral visual warning signal. These results support the claim that the introduction of peripersonal warning signals results in a significant performance advantage relative to traditionally designed warnings. Warning systems that have been designed around the constraints of the human brain offer great potential in the future design ofmultisensory interfaces.