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Alluring illusions: a comment on Kelley and Kelley

An illusion is a result of a discrepancy between the physical reality and an individual’s perception of it. Animals use their senses to form a representation of their environment, but sensory information and its processing are not free of constraints. For example, to form a representation of the 3D reality, our visual system constructs the missing third dimension from the 2D projection of the environment on our retinas. Usually there are many possible 3D interpretations for a given retinal projection, and sometimes our representation of reality is based on an incorrect interpretation. Protective coloration is one of the fields where illusions may be particularly important. Color patterns of many prey species decrease the amount of visual information emitted or induce false interpretation of it to manipulate predators’ impression of the presence or the appearance of the prey. Predators’ perception of the cues and signals emitted by a prey is an important determinant of prey survival. Therefore, signals and cues may be selected to make use of shortcomings in the predator’s perception. Also, behavioral adaptations can contribute to this. For example, background preference by prey can in various ways increase the probability of the prey being perceived by predators as a part of the background (Kjernsmo and Merilaita 2012). Some classic categories of protective coloration, such as disruptive coloration, have been formed on the basis of appearance and assumed optical effects of the coloration that would correspond to multiple, potentially conflicting selection pressures (Stevens and Merilaita 2009). Such indistinctness is problematic for evolutionary research of color patterns. To understand natural selection imposed on protective coloration, we would ideally need to focus on the function of coloration and the perceptual mechanisms it targets. In their review, Kelley and Kelley (2014) focus on animal communication, mainly protective coloration and sexual signaling, and use the concept of illusions to approach these adaptations. A skeptic may worry that the risk that promotion of an umbrella term, such as “deception” or “illusions,” might only results in relabeling and reclassification of previous knowledge and concepts and possibly generate a hype, in the worst case the only positive effects being limited within publication statistics. It may, however, also induce a scientifically fruitful process. Such new perspective may help to generate novel hypotheses and point new directions for research by helping to identify and bring together common denominators between topics that previously have not been considered jointly (e.g., How and Zanker 2014). The main benefit of the use of the concept illusions is that it shifts our focus onto perception and cognitive processes that underlie the adaptations of animal communication. As the review points out, this is not a new insight. For example, many forms of protective coloration have traditionally been assumed to rely on predators’ way of perceiving the physical reality and any weaknesses therein. Despite this awareness, when the research on visual antipredator coloration has dealt with cognition, it has often focused only on the early stages of visual perception, typically photoreceptor sensitivities, whereas higher level processes have received much less attention. A central message of this review is that there is much more to fetch from psychology about other processes of perception and cognition that are potentially relevant for behavior ecologists. The role of an illusion, however, needs to be confirmed in behavioral ecologically and taxonomically relevant setups as the occurrence and nature of illusions may differ between taxa, as the review points out. Perception is one of the most impressive products of natural selection. Illusions remind us that there are uncertainties and weaknesses associated with perceptual abilities. How these weaknesses in turn power natural selection to shape communication in and appearances of animals provides an extremely fascinating area to study. This review urges us to tackle these questions and shows that there exists much knowledge that can be used to generate new, unexplored hypotheses.