Understanding insect colour constancy Werner, Annette
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
10/2022, Letnik:
377, Številka:
1862
Journal Article
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Colour constancy is the ability to recognize the colour of objects despite spectral changes in the natural illumination. As such, this phenomenon is important for most organisms with good colour ...vision, and it has been intensively studied in humans and primates. Colour constancy is also documented for several species of insects, which is not surprising given the ecological importance of colour vision. But how do insects, with their small brains, solve the complex problem of colour vision and colour constancy? In an interspecies approach, this review reports on behavioural studies on colour constancy in bees, butterflies, moths and humans, corresponding computational models and possible neurophysiological correlates.
This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.
Honeybees (Apis mellifera) discriminate multiple object features such as colour, pattern and 2D shape, but it remains unknown whether and how bees recover three-dimensional shape. Here we show that ...bees can recognize objects by their three-dimensional form, whereby they employ an active strategy to uncover the depth profiles. We trained individual, free flying honeybees to collect sugar water from small three-dimensional objects made of styrofoam (sphere, cylinder, cuboids) or folded paper (convex, concave, planar) and found that bees can easily discriminate between these stimuli. We also tested possible strategies employed by the bees to uncover the depth profiles. For the card stimuli, we excluded overall shape and pictorial features (shading, texture gradients) as cues for discrimination. Lacking sufficient stereo vision, bees are known to use speed gradients in optic flow to detect edges; could the bees apply this strategy also to recover the fine details of a surface depth profile? Analysing the bees' flight tracks in front of the stimuli revealed specific combinations of flight maneuvers (lateral translations in combination with yaw rotations), which are particularly suitable to extract depth cues from motion parallax. We modelled the generated optic flow and found characteristic patterns of angular displacement corresponding to the depth profiles of our stimuli: optic flow patterns from pure translations successfully recovered depth relations from the magnitude of angular displacements, additional rotation provided robust depth information based on the direction of the displacements; thus, the bees flight maneuvers may reflect an optimized visuo-motor strategy to extract depth structure from motion signals. The robustness and simplicity of this strategy offers an efficient solution for 3D-object-recognition without stereo vision, and could be employed by other flying insects, or mobile robots.
Color constancy refers to our remarkable ability to perceive the color of objects nearly constant despite considerable changes in the spectral content of the illumination. As such it is most ...important for object recognition. Visual motion can make object recognition harder because it limits the viewing time and increases the likelihood that an object encounters illumination changes. However, color constancy, as human color perception in general, has long been thought to be "motion blind." Here I show that, on the contrary, human color constancy is influenced by motion and improves when a color surface moves. Psychophysical experiments revealed that color constancy is influenced specifically by slow object motion and depends on the saliency of the moving figure. These surprising findings cannot be explained by low-level co-processing of color and motion signals. Instead they demonstrate a previously unknown influence of attention-driven, high-level motion processes on cortical color computation. Since motion is a frequent aspect of natural visual scenes, the synergistic integration of color and motion signals is an important mechanism for improving color identification. The new findings speak against a strict segregation of color and motion processing in the human visual cortex and suggest a network for encoding object color, which includes specialized ventral as well as dorsal visual areas.
In previous studies of image evaluation using wide color gamut displays, it is unclear to what degree people prefer the chroma‐varying images, especially the images that are more saturated than the ...most preferred image. Here, we present a study using a wide color gamut display, which measured viewers' most preferred level of image chroma (experiment 1) and their subjective evaluation of images that were less or more saturated than the previously most preferred one (experiment 2). The results showed that (a) the subjects' preferences for the original or for more saturated images depended on the images' original chroma and (b) the subjective evaluation of the images, that is, Valence and Arousal, did not deteriorate when the chroma of images increased more than the most preferred level. Such results indicate that the increase of the image chroma in wider color gamut displays can have a substantial influence on the impression images have on viewers.
•Spatially tuned chromatic adaptation supports scene segmentation in colour constancy.•Fast and region-specific adaptation supports colour constancy during visual search.•Slow adaptation to ambient ...illumination supports global colour constancy.•Fast middle-wavelength adaptation compensates for interreflections and background in natural scenes.
Illumination in natural scenes changes at multiple temporal and spatial scales: slow changes in global illumination occur in the course of a day, and we encounter fast and localised illumination changes when visually exploring the non-uniform light field of three-dimensional scenes; in addition, very long-term chromatic variations may come from the environment, like for example seasonal changes. In this context, I consider the temporal and spatial properties of chromatic adaptation and discuss their functional significance for colour constancy in three-dimensional scenes. A process of fast spatial tuning in chromatic adaptation is proposed as a possible sensory mechanism for linking colour constancy to the spatial structure of a scene. The observed middlewavelength selectivity of this process is particularly suitable for adaptation to the mean chromaticity and the compensation of interreflections in natural scenes. Two types of sensory colour constancy are distinguished, based on the functional differences of their temporal and spatial scales: a slow type, operating at a global scale for the compensation of the ambient illumination; and a fast colour constancy, which is locally restricted and well suited to compensate region-specific variations in the light field of three dimensional scenes.
Abstract
We use Scholze’s framework of diamonds to gain new insights in correspondences between $p$-adic vector bundles and local systems. Such correspondences arise in the context of $p$-adic ...Simpson theory in the case of vanishing Higgs fields. In the present paper, we provide a detailed analysis of local systems on diamonds for the étale, pro-étale, and the $v$-topology and study the structure sheaves for all three topologies in question. Applied to proper adic spaces of finite type over $\mathbb {C}_p$, this enables us to prove a category equivalence between $\mathbb {C}_p$-local systems with integral models, and modules under the $v$-structure sheaf that modulo each $p^n$ can be trivialized on a proper cover. The flexibility of the $v$-topology together with a descent result on integral models of local systems allows us to prove that the trivializability condition in the module category may be checked on any normal proper cover. This result leads to an extension of the parallel transport theory by Deninger and the second author to vector bundles with numerically flat reduction on a proper normal cover. 2020 MSC: 14G45, 14G22, 11G25.
We relate some features of Bruhat-Tits buildings and their compactifications to tropical geometry. If
G
is a semisimple group over a suitable non-Archimedean field, the stabilizers of points in the ...Bruhat-Tits building of
G
and in some of its compactifications are described by tropical linear algebra. The compactifications we consider arise from algebraic representations of
G
. We show that the fan which is used to compactify an apartment in this theory is given by the weight polytope of the representation and that it is related to the tropicalization of the hypersurface given by the character of the representation.
Given a split semisimple group over a local field, we consider the maximal
Satake-Berkovich compactification of the corresponding Euclidean building. We
prove that it can be equivariantly identified ...with the compactification which
we get by embedding the building in the Berkovich analytic space associated to
the wonderful compactification of the group. The construction of this embedding
map is achieved over a general non-archimedean complete ground field. The
relationship between the structures at infinity, one coming from strata of the
wonderful compactification and the other from Bruhat-Tits buildings, is also
investigated.
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