Edge enhancement improves disruptive camouflage by emphasising false edges and creating pictorial relief

Reconstructing illusory camouflage patterns on moth wings using computer vision

Monocular depth cues, such as shading, are fundamental for resolving three-dimensional information, such as an object's shape. Animal colour patterns may potentially exploit this mechanism of depth perception, generating false illusions for functions such as camouflage. Reconstructing the potential percept produced by false depth cues is challenging, especially for non-human, animal viewers. Here, we provide a novel step towards solving this problem, taking advantage of state-of-the-art computer vision algorithms typically used for three-dimensional scene reconstruction. We used two approaches for single-image monocular depth estimation: intrinsic image decomposition and deep learning. We first examined how these models performed using images of natural three-dimensional surfaces that moth wing patterns may mimic. We then applied these models to the wing patterns of six species of moth (Lepidoptera) with varying amounts of potential depth information. For one species, we then performed a multi-view reconstruction of the wing pattern to reveal the true (flat) wing shape. Intrinsic image decomposition, which is based on Retinex theory, was sensitive to both real depth cues and high contrast patterns, while the deep-learning models only responded to moths with strong pictorial depth cues. Both approaches reveal how the interpretation of visual cues depends not only on the information available, but also on experience with the natural world.

Smart Polydimethylsiloxane Materials: Versatility for Electrical and Electronic Devices Applications

Bio-inspired autonomous smart polydimethylsiloxane (PDMS) and its composite materials hold immense promise for a wide range of applications in electrical and electronic devices. These materials mimic natural protective mechanisms with self-healing, self-reporting, and self-cleaning properties, enabling innovative and efficient device design. Smart PDMS materials autonomously activate repair mechanisms in response to mechanical or electrical damage, achieving rapid structural and functional recovery and preventing failure due to the accumulation of minor damage. These materials can intuitively report their status through striking color changes, fluorescence, or luminescence when exposed to external stimuli, providing efficient and practical visual feedback for device health monitoring and fault warning. They also have the capacity to effectively eliminate contaminants and ice deposits from their surfaces, thereby ensuring stable device operation. This review aims to introduce the current research progress in self-healing, self-cleaning, and self-reporting PDMS materials. The review systematically discusses the principles, methodological innovations, mechanistic analysis, and applications of these materials, highlighting their significant potential for applications in the field of electrical and electronic devices. Moreover, the review provides an in-depth analysis of the key challenges facing current research and offers insights into future research directions and strategies.

Edge enhancement in three-dimensional vortex imaging based on FINCH by Bessel-like spiral phase modulation

Edge enhancement, as an important part of image processing, has played an essential role in amplitude-contrast and phase-contrast object imaging. The edge enhancement of three-dimensional (3D) vortex imaging has been successfully implemented by Fresnel incoherent correlation holography (FINCH), but the background noise and image contrast effects are still not satisfactory. To solve these issues, the edge enhancement of FINCH by employing Bessel-like spiral phase modulation is proposed and demonstrated. Compared with the conventional spiral phase modulated FINCH, the proposed technique can achieve high-quality edge enhancement 3D vortex imaging with lower background noise, higher contrast and resolution. The significantly improved imaging quality is mainly attributed to the effective sidelobes' suppression in the generated optical vortices with the Bessel-like modulation technique. Experimental results of the small circular aperture, resolution target, and the Drosophila melanogaster verify its excellent imaging performance. Moreover, we also proposed a new method for selective edge enhancement of 3D vortex imaging by breaking the symmetry of the spiral phase in the algorithmic model of isotropic edge enhancement. The reconstructed images of the circular aperture show that the proposed method is able to enhance the edges of the given objects selectively in any desired direction.

First documentation on herpetofauna diversity in Gunung Belumut Amenity Forest, Peninsular Malaysia: Implications for conservation in an Environmentally Sensitive Area (ESA)

Malaysia is blessed with lush tropical rainforests that harbour an exceptional diversity of amphibians and reptiles. However, compared to other animal groups, amphibians and reptiles have received limited attention in research, despite their ecological significance. With amphibians and reptile species having been declining rapidly due to anthropogenic activities, there is a pressing need to conserve these species and their habitats. Environmentally Sensitive Areas (ESAs) are designated regions that are beneficial due to their critical role in providing essential ecosystem services and serving as repositories of biodiversity. Nonetheless, the classification of ESAs in Malaysia lacks biological elements and only focuses on physical attributes. To enhance the current ESA classification framework by integrating biological components, there is an urgent need to obtain information on diversity and habitat in Malaysia. Therefore, the objectives of this study were twofold: to determine the diversity of amphibians and reptiles in Gunung Belumut Amenity Forest and to conduct a comparative analysis between the herpetofauna assemblages in Gunung Belumut with other forest reserves in Peninsular Malaysia. The survey was carried out between March and June 2022, with additional sampling conducted in February 2023. The Visual Encounter Survey (VES) and pitfall trap methods were employed to survey the herpetofauna species, focusing on both aquatic and terrestrial habitats within the study area. A total of 210 individuals representing 38 species of herpetofauna were recorded, comprising 18 amphibian and 20 reptile species. Amongst the observed species, Limnonectesblythii was the most frequently encountered amphibian, with 59 individuals observed, while the dominant reptile species was Cyrtodactylusconsobrinus, represented by eight individuals. This pioneering study serves as a vital baseline documentation of the amphibian and reptile assemblages in Gunung Belumut Amenity Forest. It provides valuable information for identifying extant herpetofauna species, including those of potential conservation concern or rarity. These findings contribute to ongoing conservation efforts dedicated to the preservation of herpetofauna within the region. By understanding the diversity and distribution patterns of amphibians and reptiles in Gunung Belumut, effective conservation strategies can be developed to protect these species and their habitats.

Camouflage using three-dimensional surface disruption

Disruptive markings are common in animal patterns and can provide camouflage benefits by concealing the body's true edges and/or by breaking the surface of the body into multiple depth planes. Disruptive patterns that are accentuated by high contrast borders are most likely to provide false depth cues to enhance camouflage, but studies to date have used visual detection models or humans as predators. We presented three-dimensional-printed moth-like targets to wild bird predators to determine whether: (1) three-dimensional prey with disrupted body surfaces have higher survival than three-dimensional prey with continuous surfaces, (2) two-dimensional prey with disruptive patterns or enhanced edge markings have higher survival than non-patterned two-dimensional prey. We found a survival benefit for three-dimensional prey with disrupted surfaces, and a significant effect of mean wing luminance. There was no evidence that false depth cues provided the same protective benefits as physical surface disruption in three-dimensional prey, perhaps because our treatments did not mimic the complexity of patterns found in natural animal markings. Our findings indicate that disruption of surface continuity is an important strategy for concealing a three-dimensional body shape.

Pattern variation is linked to anti-predator coloration in butterfly larvae

Prey animals typically try to avoid being detected and/or advertise to would-be predators that they should be avoided. Both anti-predator strategies primarily rely on colour to succeed, but the specific patterning used is also important. While the role of patterning in camouflage is relatively clear, the design features of aposematic patterns are less well understood. Here, we use a comparative approach to investigate how pattern use varies across a phylogeny of 268 species of cryptic and aposematic butterfly larvae, which also vary in social behaviour. We find that longitudinal stripes are used more frequently by cryptic larvae, and that patterns putatively linked to crypsis are more likely to be used by solitary larvae. By contrast, aposematic larvae are more likely to use horizontal bands and spots, but we find no differences in the use of individual pattern elements between solitary and gregarious aposematic species. However, solitary aposematic larvae are more likely to display multiple pattern elements, whereas those with no pattern are more likely to be gregarious. Our study advances our understanding of how pattern variation, coloration and social behaviour covary across lepidopteran larvae, and highlights new questions about how patterning affects larval detectability and predator responses to aposematic prey.

CamoEvo: An open access toolbox for artificial camouflage evolution experiments

Camouflage research has long shaped our understanding of evolution by natural selection, and elucidating the mechanisms by which camouflage operates remains a key question in visual ecology. However, the vast diversity of color patterns found in animals and their backgrounds, combined with the scope for complex interactions with receiver vision, presents a fundamental challenge for investigating optimal camouflage strategies. Genetic algorithms (GAs) have provided a potential method for accounting for these interactions, but with limited accessibility. Here, we present CamoEvo, an open-access toolbox for investigating camouflage pattern optimization by using tailored GAs, animal and egg maculation theory, and artificial predation experiments. This system allows for camouflage evolution within the span of just 10-30 generations (∼1-2 min per generation), producing patterns that are both significantly harder to detect and that are optimized to their background. CamoEvo was built in ImageJ to allow for integration with an array of existing open access camouflage analysis tools. We provide guides for editing and adjusting the predation experiment and GA as well as an example experiment. The speed and flexibility of this toolbox makes it adaptable for a wide range of computer-based phenotype optimization experiments.

3D animal camouflage

Camouflage is a fundamental way for animals to avoid detection and recognition. While depth information is critical for object detection and recognition, little is known about how camouflage patterns might interfere with the mechanisms of depth perception. We reveal how many common camouflage strategies could exploit 3D visual processing mechanisms.

The ecology of sleep in non-avian reptiles

Sleep is ubiquitous in the animal kingdom and yet displays considerable variation in its extent and form in the wild. Ecological factors, such as predation, competition, and microclimate, therefore are likely to play a strong role in shaping characteristics of sleep. Despite the potential for ecological factors to influence various aspects of sleep, the ecological context of sleep in non-avian reptiles remains understudied and without systematic direction. In this review, we examine multiple aspects of reptilian sleep, including (i) habitat selection (sleep sites and their spatio-temporal distribution), (ii) individual-level traits, such as behaviour (sleep postures), morphology (limb morphometrics and body colour), and physiology (sleep architecture), as well as (iii) inter-individual interactions (intra- and inter-specific). Throughout, we discuss the evidence of predation, competition, and thermoregulation in influencing sleep traits and the possible evolutionary consequences of these sleep traits for reptile sociality, morphological specialisation, and habitat partitioning. We also review the ways in which sleep ecology interacts with urbanisation, biological invasions, and climate change. Overall, we not only provide a systematic evaluation of the conceptual and taxonomic biases in the existing literature on reptilian sleep, but also use this opportunity to organise the various ecological hypotheses for sleep characteristics. By highlighting the gaps and providing a prospectus of research directions, our review sets the stage for understanding sleep ecology in the natural world.

Finding a signal hidden among noise: how can predators overcome camouflage strategies?

Substantial progress has been made in the past 15 years regarding how prey use a variety of visual camouflage types to exploit both predator visual processing and cognition, including background matching, disruptive coloration, countershading and masquerade. By contrast, much less attention has been paid to how predators might overcome these defences. Such strategies include the evolution of more acute senses, the co-opting of other senses not targeted by camouflage, changes in cognition such as forming search images, and using behaviours that change the relationship between the cryptic individual and the environment or disturb prey and cause movement. Here, we evaluate the methods through which visual camouflage prevents detection and recognition, and discuss if and how predators might evolve, develop or learn counter-adaptations to overcome these.

This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests'.

False holes as camouflage

Long noted by naturalists, leaf mimicry provides some of the most impressive examples of camouflage through masquerade. Many species of leaf-mimicking Lepidoptera also sport wing markings that closely resemble irregularly shaped holes caused by decay or insect damage. Despite proposals that such markings can either enhance resemblance to damaged leaves or act to disrupt surface appearance through false depth cues, to our knowledge, no attempt has been made to establish exactly how these markings function, or even whether they confer a survival benefit to prey. Here, in two field experiments using artificial butterfly-like targets, we show that false hole markings provide significant survival benefits against avian predation. Furthermore, in a computer-based visual search experiment, we demonstrate that detection of such targets by humans is impeded in a similar fashion. Equally contrasting light marks do not have the same effect; indeed, they lead to increased detection. We conclude that the mechanism is the disruption of the otherwise homogeneous wing surface (surface disruptive camouflage) and that, by resembling the holes sometimes found in real leaves, the disruptive benefits are not offset by conspicuousness costs.

Ecological, behavioral, and phylogenetic influences on the evolution of dorsal color pattern in geckos

The dorsal surfaces of many taxonomic groups often feature repetitive pattern elements consisting of stripes, spots, or bands. Here, we investigate how distinct categories of camouflage pattern work by relating them to ecological and behavioral traits in 439 species of gecko. We use phylogenetic comparative methods to test outstanding hypotheses based on camouflage theory and research in other taxa. We found that bands are associated with nocturnal activity, suggesting bands provide effective camouflage for motionless geckos resting in refugia during the day. A predicted association between stripes and diurnal activity was not supported, suggesting that stripes do not work via dazzle camouflage mechanisms in geckos. This, along with a lack of support for our prediction that plain patterning should be associated with open habitats, suggests that similar camouflage patterns do not work in consistent ways across taxa. We also found that plain and striped lineages frequently switched between using open or closed habitats, whereas spotted lineages rarely transitioned. This suggests that pattern categories differ in how specialized or generalized their camouflage is. This result has ramifications for theory on how camouflage compromises to background heterogeneity and how camouflage pattern might influence evolutionary trajectories.

Edge-Enhanced Disruptive Camouflage Impairs Shape Discrimination

Disruptive colouration (DC) is a form of camouflage comprised of areas of pigmentation across a target's surface that form false edges, which are said to impede detection by disguising the outline of the target. In nature, many species with DC also exhibit edge enhancement (EE); light areas have lighter edges and dark areas have darker edges. EE DC has been shown to undermine not only localisation but also identification of targets, even when they are not hidden (Sharman, Moncrieff, & Lovell, 2018). We use a novel task, where participants judge which "snake" is more "wiggly," to measure shape discrimination performance for three colourations (uniform, DC, and EE DC) and two backgrounds (leafy and uniform). We show that EE DC impairs shape discrimination even when targets are not hidden in a textured background. We suggest that this mechanism may contribute to misidentification of EE DC targets.

A Pixel-Encoder Retinal Ganglion Cell with Spatially Offset Excitatory and Inhibitory Receptive Fields

The spike trains of retinal ganglion cells (RGCs) are the only source of visual information to the brain. Here, we genetically identify an RGC type in mice that functions as a pixel encoder and increases firing to light increments (Pix_ON-RGC). Pix_ON-RGCs have medium-sized dendritic arbors and non-canonical center-surround receptive fields. From their receptive field center, Pix_ON-RGCs receive only excitatory input, which encodes contrast and spatial information linearly. From their receptive field surround, Pix_ON-RGCs receive only inhibitory input, which is temporally matched to the excitatory center input. As a result, the firing rate of Pix_ON-RGCs linearly encodes local image contrast. Spatially offset (i.e., truly lateral) inhibition of Pix_ON-RGCs arises from spiking GABAergic amacrine cells. The receptive field organization of Pix_ON-RGCs is independent of stimulus wavelength (i.e., achromatic). Pix_ON-RGCs project predominantly to the dorsal lateral geniculate nucleus (dLGN) of the thalamus and likely contribute to visual perception.

Disruptive coloration and binocular disparity: breaking camouflage

Many species employ camouflage to disguise their true shape and avoid detection or recognition. Disruptive coloration is a form of camouflage in which high-contrast patterns obscure internal features or break up an animal's outline. In particular, edge enhancement creates illusory, or 'fake' depth edges within the animal's body. Disruptive coloration often co-occurs with background matching, and together, these strategies make it difficult for an observer to visually segment an animal from its background. However, stereoscopic vision could provide a critical advantage in the arms race between perception and camouflage: the depth information provided by binocular disparities reveals the true three-dimensional layout of a scene, and might, therefore, help an observer to overcome the effects of disruptive coloration. Human observers located snake targets embedded in leafy backgrounds. We analysed performance (response time) as a function of edge enhancement, illumination conditions and the availability of binocular depth cues. We confirm that edge enhancement contributes to effective camouflage: observers were slower to find snakes whose patterning contains 'fake' depth edges. Importantly, however, this effect disappeared when binocular depth cues were available. Illumination also affected detection: under directional illumination, where both the leaves and snake produced strong cast shadows, snake targets were localized more quickly than in scenes rendered under ambient illumination. In summary, we show that illusory depth edges, created via disruptive coloration, help to conceal targets from human observers. However, cast shadows and binocular depth information improve detection by providing information about the true three-dimensional structure of a scene. Importantly, the strong interaction between disparity and edge enhancement suggests that stereoscopic vision has a critical role in breaking camouflage, enabling the observer to overcome the disruptive effects of edge enhancement.

Dissociating the effect of disruptive colouration on localisation and identification of camouflaged targets

Disruptive camouflage features contrasting areas of pigmentation across the animals’ surface that form false edges which disguise the shape of the body and impede detection. In many taxa these false edges feature local contrast enhancement or edge enhancement, light areas have lighter edges and dark areas have darker edges. This additional quality is often overlooked in existing research. Here we ask whether disruptive camouflage can have benefits above and beyond concealing location. Using a novel paradigm, we dissociate the time courses of localisation and identification of a target in a single experiment. We measured the display times required for a stimulus to be located or identified (the critical duration). Targets featured either uniform, disruptive or edge enhanced disruptive colouration. Critical durations were longer for identifying targets with edge enhanced disruptive colouration camouflage even when presented against a contrasting background, such that all target types were located equally quickly. For the first time, we establish empirically that disruptive camouflage not only conceals location, but also disguises identity. This shows that this form of camouflage can be useful even when animals are not hidden. Our findings offer insights into how edge enhanced disruptive colouration undermines visual perception by disrupting object recognition.

Edge enhancement improves disruptive camouflage by emphasising false edges and creating pictorial relief

Disruptive colouration is a visual camouflage composed of false edges and boundaries. Many disruptively camouflaged animals feature enhanced edges; light patches are surrounded by a lighter outline and/or a dark patches are surrounded by a darker outline. This camouflage is particularly common in amphibians, reptiles and lepidopterans. We explored the role that this pattern has in creating effective camouflage. In a visual search task utilising an ultra-large display area mimicking search tasks that might be found in nature, edge enhanced disruptive camouflage increases crypsis, even on substrates that do not provide an obvious visual match. Specifically, edge enhanced camouflage is effective on backgrounds both with and without shadows; i.e. this is not solely due to background matching of the dark edge enhancement element with the shadows. Furthermore, when the dark component of the edge enhancement is omitted the camouflage still provided better crypsis than control patterns without edge enhancement. This kind of edge enhancement improved camouflage on all background types. Lastly, we show that edge enhancement can create a perception of multiple surfaces. We conclude that edge enhancement increases the effectiveness of disruptive camouflage through mechanisms that may include the improved disruption of the object outline by implying pictorial relief.