Visual salience and biological motion interact to determine camouflaged target detectability

In the corner of the eye: camouflaging motion in the peripheral visual field

Most animals need to move, and motion will generally break camouflage. In many instances, most of the visual field of a predator does not fall within a high-resolution area of the retina and so, when an undetected prey moves, that motion will often be in peripheral vision. We investigate how this can be exploited by prey, through different patterns of movement, to reduce the accuracy with which the predator can locate a cryptic prey item when it subsequently orients towards a target. The same logic applies for a prey species trying to localize a predatory threat. Using human participants as surrogate predators, tasked with localizing a target on peripherally viewed computer screens, we quantify the effects of movement (duration and speed) and target pattern. We show that, while motion is certainly detrimental to camouflage, should movement be necessary, some behaviours and surface patterns reduce that cost. Our data indicate that the phenotype that minimizes localization accuracy is unpatterned, having the mean luminance of the background, does not use a startle display prior to movement, and has short (below saccadic latency), fast movements.

What makes motion dazzle markings effective against predation?

Motion dazzle markings comprise patterns such as stripes and zig-zags that are postulated to protect moving prey by making predators misjudge the prey’s speed or trajectory. Recent experiments have provided conflicting results on their effect on speed perception and attack success. We focus on motion dazzle stripes and investigate the influence of four parameters—stripe orientation, stripe contrast, target size, and target speed—on perceived speed and attack success using a common experimental paradigm involving human “predators” attacking virtual moving targets on a computer touchscreen. We found that high-contrast stripes running parallel or perpendicular to the direction of motion reduce attack success compared to conspicuous uniform targets. Surprisingly, parallel stripes induced underestimation of speed, while perpendicular stripes induced overestimation of speed in relation to uniform black, suggesting that misjudgment of speed per se is sufficient to reduce attack accuracy. Across all the experiments, we found some support for parallel stripes inducing underestimation of target speed but these stripes reduced attack success only when targets were small, moved at an intermediate speed, and had high internal contrast. We suggest that prey features (e.g., size or speed) are an important determinant of capture success and that distortion of speed perception by a color pattern does not necessarily translate to reduced capture success of the prey. Overall, our results support the idea that striped patterns in prey animals can reduce capture in motion but are effective under a limited set of conditions.

Camouflage pattern features interact with movement speed to determine human target detectability

Applied ergonomics research examines not only the fit, form and function of military uniforms, but also their ability to effectively camouflage personnel as they perform job-related tasks. Many of these job-related tasks involve moving through environments, but existing literature examining camouflage effectiveness often assumes that movement effectively "breaks" even the best camouflage patterns, rendering them of limited utility for reducing the visual signature of a moving target. However, recent research demonstrates that animals equipped with adaptive camouflage change their patterning in predictable ways during movement and this adaptation decreases detectability, suggesting that uniform patterning may still hold value for reducing conspicuity during movement. The present experiment examined whether three visual pattern characteristics, local contrast, orientation, and spatial frequency, would influence the detectability of a moving human target. Participants attempted to detect and localize a simulated human target moving across a background scene, and a factorial design varied target movement speed, and the local contrast, spatial frequency, and orientation of its camouflage patterning. Results showed that target detectability was strongly influenced by target movement rate, pattern local contrast, and pattern spatial frequency, and these effects persisted even under conditions of very fast movement. Importantly, we found that the effect of local contrast was most robust under conditions of movement, suggesting its importance for reducing detectability of moving personnel. We conclude that movement is not always sufficient to break the concealment offered by a pattern with low contrast and a spatial frequency match with its background. Results are discussed in the context of visual processing theories and the application of these findings to the design and development of static and adaptive camouflage patterns for military personnel.