Computation of Texture and Stereoscopic Depth in Humans

The computation of texture and of stereoscopic depth is limited by a number of factors in the design of the optical front-end and subsequent processing stages in humans and machines. A number of limiting factors in the human visual system, such as resolution of the optics and opto-electronic interface, contrast, luminance, temporal resolution and eccentricity are reviewed and evaluated concerning their relevance for the recognition of texture and stereoscopic depth. The algorithms used by the human brain to discriminate between textures and to compute stereoscopic depth are very fast and efficient. Their study might be beneficial for the development of better algorithms in machine vision

Evidence for aggressive mimicry in an adult brood parasitic bird, and generalized defences in its host.

Mimicry of a harmless model (aggressive mimicry) is used by egg, chick and fledgling brood parasites that resemble the host's own eggs, chicks and fledglings. However, aggressive mimicry may also evolve in adult brood parasites, to avoid attack from hosts and/or manipulate their perception of parasitism risk. We tested the hypothesis that female cuckoo finches (Anomalospiza imberbis) are aggressive mimics of female Euplectes weavers, such as the harmless, abundant and sympatric southern red bishop (Euplectes orix). We show that female cuckoo finch plumage colour and pattern more closely resembled those of Euplectes weavers (putative models) than Vidua finches (closest relatives); that their tawny-flanked prinia (Prinia subflava) hosts were equally aggressive towards female cuckoo finches and southern red bishops, and more aggressive to both than to their male counterparts; and that prinias were equally likely to reject an egg after seeing a female cuckoo finch or bishop, and more likely to do so than after seeing a male bishop near their nest. This is, to our knowledge, the first quantitative evidence for aggressive mimicry in an adult bird, and suggests that host-parasite coevolution can select for aggressive mimicry by avian brood parasites, and counter-defences by hosts, at all stages of the reproductive cycle.W.E.F. was funded by the Australian National University Research School of Biology studentship, and an Endeavour Research Fellowship; C.N.S. was funded by a Royal Society Dorothy Hodgkin Fellowship, a BBSRC David Phillips Research Fellowship (BB/J014109/1) and the DST-NRF Centre of Excellence at the Percy FitzPatrick Institute; and N.E.L. was funded by the Australian Research Council.This is the final version of the article. It first appeared from Royal Society Publishing via http://dx.doi.org/10.1098/rspb.2015.07

Does the use of nest materials in a ground-nesting bird result from a compromise between the risk of egg overheating and camouflage?

Many studies addressing the use of nest materials by animals have focused on only one factor to explain its function. However, the consideration of more than one factor could explain the apparently maladaptive choice of nest materials that make nests conspicuous to predators. We experimentally tested whether there is a trade-off in the use of nest materials between the risks of egg predation versus protection from overheating. We studied the ground-nesting Kentish plover, Charadrius alexandrinus, in southern Spain. We added materials differing in thermal properties and coloration to the nests, thus affecting rates of egg heating, nest temperature and camouflage. Before these manipulations, adults selected materials that were lighter than the microhabitat, probably to buffer the risk of egg overheating. However, the adults did not keep the lightest experimental materials, probably because they reduced camouflage, and this could make the nests even more easily detectable to predators. In all nests, adults removed most of the experimental materials independently of their properties, so that egg camouflage returned to the original situation within a week of the experimental treatments. Although the thermal environment may affect the choice of nest materials by plovers, ambient temperatureswere not so high at our study site as to determine the acceptance of the lightest experimental materials

Fidelity metrics for virtual environment simulations based on spatial memory awareness states

This paper describes a methodology based on human judgments of memory awareness states for assessing the simulation fidelity of a virtual environment (VE) in relation to its real scene counterpart. To demonstrate the distinction between task performance-based approaches and additional human evaluation of cognitive awareness states, a photorealistic VE was created. Resulting scenes displayed on a headmounted display (HMD) with or without head tracking and desktop monitor were then compared to the real-world task situation they represented, investigating spatial memory after exposure. Participants described how they completed their spatial recollections by selecting one of four choices of awareness states after retrieval in an initial test and a retention test a week after exposure to the environment. These reflected the level of visual mental imagery involved during retrieval, the familiarity of the recollection and also included guesses, even if informed. Experimental results revealed variations in the distribution of participants’ awareness states across conditions while, in certain cases, task performance failed to reveal any. Experimental conditions that incorporated head tracking were not associated with visually induced recollections. Generally, simulation of task performance does not necessarily lead to simulation of the awareness states involved when completing a memory task. The general premise of this research focuses on how tasks are achieved, rather than only on what is achieved. The extent to which judgments of human memory recall, memory awareness states, and presence in the physical and VE are similar provides a fidelity metric of the simulation in question

Fitness costs associated with building and maintaining the burying beetle's carrion nest

It is well-known that features of animal nest architecture can be explained by fitness benefits gained by the offspring housed within. Here we focus on the little-tested suggestion that the fitness costs associated with building and maintaining a nest should additionally account for aspects of its architecture. Burying beetles prepare an edible nest for their young from a small vertebrate carcass, by ripping off any fur or feathers and rolling the flesh into a rounded ball. We found evidence that only larger beetles are able to construct rounder carcass nests, and that rounder carcass nests are associated with lower maintenance costs. Offspring success, however, was not explained by nest roundness. Our experiment thus provides rare support for the suggestion that construction and maintenance costs are key to understanding animal architecture.Cambridge Trust, CONACyT, European Research Council (Consolidators Grant ID: 310785 BALDWINIAN_BEETLES), Royal Society (Wolfson Merit Award), Natural Environment Research Council (Grant ID: NE/H019731/1

Camouflage predicts survival in ground-nesting birds

ArticleEvading detection by predators is crucial for survival. Camouflage is therefore a widespread adaptation, but despite substantial research effort our understanding of different camouflage strategies has relied predominantly on artificial systems and on experiments disregarding how camouflage is perceived by predators. Here we show for the first time in a natural system, that survival probability of wild animals is directly related to their level of camouflage as perceived by the visual systems of their main predators. Ground-nesting plovers and coursers flee as threats approach, and their clutches were more likely to survive when their egg contrast matched their surrounds. In nightjars – which remain motionless as threats approach – clutch survival depended on plumage pattern matching between the incubating bird and its surrounds. Our findings highlight the importance of pattern and luminance based camouflage properties, and the effectiveness of modern techniques in capturing the adaptive properties of visual phenotypes.BBSRCRoyal Society Dorothy Hodgkin FellowshipDST-NRF Centre of Excellence at the Percy FitzPatrick Institut

Escape distance in ground-nesting birds differs with individual level of camouflage

This is the author accepted manuscript. The final version is available from University of Chicago Press via the DOI in this record.Camouflage is one of the most widespread anti-predator strategies in the animal kingdom, yet no animal can match its background perfectly in a complex environment. Therefore, selection should favour individuals that use information on how effective their camouflage is in their immediate habitat when responding to an approaching threat. In a field study of African ground-nesting birds (plovers, coursers, and nightjars), we tested the hypothesis that individuals adaptively modulate their escape behaviour in relation to their degree of background matching. We used digital imaging and models of predator vision to quantify differences in color, luminance, and pattern between eggs and their background, as well as the plumage of incubating adult nightjars. We found that plovers and coursers showed greater escape distances when their eggs were a poorer pattern match to the background. Nightjars sit on their eggs until a potential threat is nearby, and correspondingly they showed greater escape distances when the pattern and color match of the incubating adult's plumage, rather than its eggs, was a poorer match to the background. Finally, escape distances were shorter in the middle of the day, suggesting that escape behaviour is mediated by both camouflage and thermoregulation.In Zambia we thank the Bruce-Miller, Duckett and Nicolle families, Collins Moya and numerous other nest-finding assistants and land-owners, Lackson Chama, and the Zambia Wildlife Authority. We also thank Tony Fulford and are grateful for the helpful comments provided by Tim Caro, Innes Cuthill, Daniel Osorio, and two anonymous referees. J.T., J.W-A. and M.S. were funded by a Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/J018309/1 to M.S., and a BBSRC David Phillips Research Fellowship (BB/G022887/1) to M.S., and C.N.S was funded by a Royal Society Dorothy Hodgkin Fellowship, a BBSRC David Phillips Fellowship (BB/J014109/1) and the DST-NRF Centre of Excellence at the Percy FitzPatrick Institute

Brood parasitism is linked to egg pattern diversity within and among species of Australian passerines.

This is the final version of the article. Available from the publisher via the DOI in this record.Bird eggs show striking diversity in color and pattern. One explanation for this is that interactions between avian brood parasites and their hosts drive egg phenotype evolution. Brood parasites lay their eggs in the nests of other species, their hosts. Many hosts defend their nests against parasitism by rejecting foreign eggs, which selects for parasite eggs that mimic those of the host. In theory, this may in turn select for changes in host egg phenotypes over time to facilitate discrimination of parasite eggs. Here, we test for the first time whether parasitism by brood parasites has led to increased divergence in egg phenotype among host species. Using Australian host and nonhost species and objective measures of egg color and pattern, we show that (i) hosts of brood parasites have higher within-species variation in egg pattern than nonhosts, supporting previous findings in other systems, and (ii) host species have diverged more in their egg patterns than nonhost species after controlling for divergence time. Overall, our results suggest that brood parasitism has played a significant role in the evolution of egg diversity and that these effects are evident, not only within species, but also among species.I.M. was supported by an Australian National University Vice-Chancellor’s travel grant, and N.E.L. was supported by the Australian Research Council