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Cephalopod photoreceptors are polarisation-sensitive, giving them an ability to discriminate between lights of different angle and degree of polarisation. While colour vision is achieved by comparison of signals of photoreceptors tuned to... more
Cephalopod photoreceptors are polarisation-sensitive, giving them an ability to discriminate between lights of different angle and degree of polarisation. While colour vision is achieved by comparison of signals of photoreceptors tuned to different parts of light spectra, polarisation vision is achieved by comparison of signals of photoreceptors tuned to different orientations of e-vector. Therefore, from a theoretical point of view, polarisation vision is similar to colour vision. In particular, detection of polarised light against an unpolarised background is analogous to detection of chromatic light against grey. The dependence of polarisation contrast sensitivity on the angle of polarisation can be theoretically predicted using a receptor noise limited model in much the same way as it has been done for predicting the shape of the increment threshold spectral sensitivity in animals with colour vision. Here we report angular dependence of polarisation contrast sensitivity in octopus (O. tetricus, Gould 1852) and compare the theoretical predictions of polarisation contrast with the experimental results. Polarisation gratings were generated using LCD screens with removed polarisers and the orientation of polarisation was changed by rotating the screen. Reaction to the stimulus was recorded using a fixation reflex. We show that, in agreement with the theoretical predictions, the maximum contrast sensitivity is achieved at horizontal and vertical orientations of polarisation. Our results demonstrate that the dependence of polarisation contrast sensitivity on the angle of polarisation can be analysed in the same way as the dependence of colour thresholds on wavelength of monochromatic light added to a grey background.
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Research Interests: Computer Science, Artificial Intelligence, Computer Vision, Colour Vision, Biology, and 15 moreAnimal Behaviour, Medicine, Color Perception, Biological Sciences, Models, Animals, Color Vision, Biological, Colour measurement, Chromaticity, Experimental Biology, Luminance, Hue, Brightness, and Medical and Health Sciences
Animals use colour vision in a range of behaviours. Visual performance is limited by thresholds, which are set by noise in photoreceptors and subsequent neural processing. The receptor noise limited (RNL) model of colour discrimination is... more
Animals use colour vision in a range of behaviours. Visual performance is limited by thresholds, which are set by noise in photoreceptors and subsequent neural processing. The receptor noise limited (RNL) model of colour discrimination is widely used for modelling colour vision and accounts well for experimental data from many species. In one of the most comprehensive tests yet of colour discrimination in a non-human species, we used Ishihara-style stimulus patterns to examine thresholds for 21 directions at five locations in colour space for the fish Rhinecanthus aculeatus. Thresholds matched RNL model predictions most closely for stimuli near the achromatic point, but exceeded predictions (indicating a decline in sensitivity) with distance from this point. Thresholds were also usually higher for saturation than for hue differences. These changes in colour threshold with colour space location and direction may give insight into photoreceptor non-linearities and post-receptoral mech...
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Trichomacy in primates has long been regarded as an adaptive trait to facilitate detecting reddish objects such as ripe fruits against background leaves. Spider monkeys are excellent subjects to test this hypothesis because of their... more
Trichomacy in primates has long been regarded as an adaptive trait to facilitate detecting reddish objects such as ripe fruits against background leaves. Spider monkeys are excellent subjects to test this hypothesis because of their highly frugivorous diet and polymorphic colour vision. In this study, we examined fruit foraging behaviour of a free-ranging group of spider monkeys (Ateles geoffroyi), consisting of dichromats (N = 11) and trichromats (N = 9) in Santa Rosa National Park, Costa Rica. First, we compared the frequency, accuracy and unit-time intake efficiency of detecting fruits at close viewing distance between dichromats and trichromats. Unexpectedly, trichromats did not show any foraging advantage. This result is explained by the importance of achromatic contrast between fruits and leaves to both dichromats and trichromats. In natural conditions, olfaction could also be an informative modality in fruit foraging. We then examined whether and how sniffing behaviour was as...
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Coral reef fishes are among the most colourful animals in the world. Given the diversity of lifestyles and habitats on the reef, it is probable that in many instances coloration is a compromise between crypsis and communication. However,... more
Coral reef fishes are among the most colourful animals in the world. Given the diversity of lifestyles and habitats on the reef, it is probable that in many instances coloration is a compromise between crypsis and communication. However, human observation of this coloration is biased by our primate visual system. Most animals have visual systems that are ‘tuned’ differently to humans; optimized for different parts of the visible spectrum. To understand reef fish colours, we need to reconstruct the appearance of colourful patterns and backgrounds as they are seen through the eyes of fish. Here, the coral reef associated triggerfish, Rhinecanthus aculeatus , was tested behaviourally to determine the limits of its colour vision. This is the first demonstration of behavioural colour discrimination thresholds in a coral reef species and is a critical step in our understanding of communication and speciation in this vibrant colourful habitat. Fish were trained to discriminate between a re...
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Analysis of data to obtain octopus contrast thresholds and bootstrap procedure for quantiles
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Bees discriminate between many different colours of flower petals, but it is not well understood how they perceive and learn patterns frequently found in flowers with colourful structures. We used multi-spectral imaging to explore... more
Bees discriminate between many different colours of flower petals, but it is not well understood how they perceive and learn patterns frequently found in flowers with colourful structures. We used multi-spectral imaging to explore chromatic cues in concentric flower patterns as they are seen through the low-resolution eyes of the honeybee. We find a diversity of colour combinations, which suggests that plants might exploit the sensory capabilities of pollinators, like bees, that learn colours easily. A consistent feature is that the surround of the pattern has a stronger chromatic contrast to the foliage background than the centre. This can potentially facilitate the fast identification of floral objects within colourful scenes when a foraging bee moves through a flower patch. In behavioural experiments we trained and tested bees with three types of concentric patterns. They recognized and discriminated patterns accurately in most tests, relying flexibly on both chromatic and spatia...
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Behavioural contrast sensitivity in Octopus tetricus was measured in the range 0.05- 12 cycles per degree (cpd) using a fixation reflex. We show that the contrast sensitivity reaches its maximum (between 1% and 4%) at 0.3 cpd, and... more
Behavioural contrast sensitivity in Octopus tetricus was measured in the range 0.05- 12 cycles per degree (cpd) using a fixation reflex. We show that the contrast sensitivity reaches its maximum (between 1% and 4%) at 0.3 cpd, and decreases to approximately half of the maximum value at the lowest spatial frequency. Reduction of sensitivity at low spatial frequency is a signature of lateral inhibition in visual systems. In vertebrates and insects, lateral inhibition helps to overcome the bottleneck of encoding information into spikes. In octopus, photoreceptors generate spikes themselves and are directly connected to the brain through their axons. Therefore, the neural processing occurring in octopus brain cannot help to overcome the bottleneck of encoding information into spikes. We conclude that, in octopus, the lateral inhibition occurs either in the brain after information has been encoded into spikes, or that photoreceptors inhibit each other. This is the first time behavioural contrast sensitivity has been measured in a cephalopod
The Atacama Desert, one of the driest places on earth, holds a rich biodiversity that becomes most appreciable in years when unusual rainfall accumulation triggers a phenomenon of explosive development of ephemeral herbaceous and woody... more
The Atacama Desert, one of the driest places on earth, holds a rich biodiversity that becomes most appreciable in years when unusual rainfall accumulation triggers a phenomenon of explosive development of ephemeral herbaceous and woody desert species known as “desierto florido” or “blooming desert.” Despite the scientific importance of this unique phenomenon only few studies have addressed the mechanisms of flower phenotypic divergence under the fluctuating environment provided by this recurrent event. We investigated the mechanisms of floral color diversity in Cistanthe longiscapa (Montiaceae), a dominant species across the ephemeral blooming landscape of Atacama Desert. Our analyses show that the variation in colors of C. longiscapa flowers result from petals containing betalain pigments with different absorption spectra. The different pigment composition of petals causes flower color differences in the visible and ultraviolet (UV) range of the spectrum. Through color vision model...
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Humans group components of visual patterns according to their colour, and perceive colours separately from shape. This property of human visual perception is the basis behind the Ishihara test for colour deficiency, where an observer is... more
Humans group components of visual patterns according to their colour, and perceive colours separately from shape. This property of human visual perception is the basis behind the Ishihara test for colour deficiency, where an observer is asked to detect a pattern made up of dots of similar colour with variable lightness against a background of dots made from different colour(s) and lightness. To find out if fish use colour for object segregation in a similar manner to humans, we used stimuli inspired by the Ishihara test. Triggerfish (Rhinecanthus aculeatus) were trained to detect a cross constructed from similarly coloured dots against various backgrounds. Fish detected this cross even when it was camouflaged using either achromatic or chromatic noise, but fish relied more on chromatic cues for shape segregation. It remains unknown whether fish may switch to rely primarily on achromatic cues in scenarios where target objects have higher achromatic contrast and lower chromatic contra...
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Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, foraging and predator avoidance. However, our understanding of animal colour perception is largely derived from human psychophysics, even though... more
Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, foraging and predator avoidance. However, our understanding of animal colour perception is largely derived from human psychophysics, even though animal visual systems differ from our own. Behavioural tests of non-human animals are required to understand how colour signals are perceived by them. Here we introduce a novel test of colour vision in animals inspired by the Ishihara colour charts, which are widely used to identify human colour deficiencies. These charts consist of dots that vary in colour, brightness and size, and are designed so that a numeral or letter is distinguishable from distractor dots for humans with normal colour vision. In our method, distractor dots have a fixed chromaticity (hue and saturation) but vary in luminance. Animals can be trained to find single target dots that differ from distractor dots in chromaticity. We provide Matlab code for creating these stimuli, which can be modified for use with different animals. We demonstrate the success of this method with triggerfish, Rhinecanthus aculeatus, and highlight behavioural parameters that can be measured, including success of finding the target dot, time to detect dot and error rate. Triggerfish quickly learnt to select target dots that differed from distractors dots regardless of the particular hue or saturation, and proved to use acute colour vision. We measured discrimination thresholds by testing the detection of target colours that were of increasing colour distances (∆S) from distractor dots in different directions of colour space. At least for some colours, thresholds indicated better discrimination than expected from the Receptor Noise Limited (RNL) model assuming 5% Weber fraction for the long-wavelength cone. This methodology seems to be highly effective because it resembles natural foraging behavior for the triggerfish and may well be adaptable to a range of other animals, including mammals, birds, bees and freshwater fish. Other questions may be addressed using this methodology, including luminance thresholds, sensory bias, effects of sensory noise in detection tasks, colour categorization and salienc
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Behavioural contrast sensitivity in <i>Octopus tetricus</i> was measured in the range of 0.05–12 cycles per degree (cpd) using a fixation reflex. We show that the contrast sensitivity reaches its maximum (between 1% and 4%) at... more
Behavioural contrast sensitivity in <i>Octopus tetricus</i> was measured in the range of 0.05–12 cycles per degree (cpd) using a fixation reflex. We show that the contrast sensitivity reaches its maximum (between 1% and 4%) at 0.3 cpd, and decreases to approximately half of the maximum value at the lowest spatial frequency. Reduction of sensitivity at low spatial frequency is a signature of lateral inhibition in visual systems. In vertebrates and insects, lateral inhibition helps to overcome the bottleneck of encoding information into spikes. In octopus, photoreceptors generate spikes themselves and are directly connected to the brain through their axons. Therefore, the neural processing occurring in octopus brain cannot help to overcome the bottleneck of encoding information into spikes. We conclude that, in octopus, the lateral inhibition occurs either in the brain after information has been encoded into spikes, or that photoreceptors inhibit each other. This is the fi...
Method details outlining data processing and measurements of false alarm rates and blind responses
Supplementary Figure. 3. Training session performance with proportion of correct choices (Pcor) recorded for individuals (Fish ID) from fish which learnt the yellow cross (a and b) and fish which learnt the blue cross (c and d). The... more
Supplementary Figure. 3. Training session performance with proportion of correct choices (Pcor) recorded for individuals (Fish ID) from fish which learnt the yellow cross (a and b) and fish which learnt the blue cross (c and d). The dashed-line marks a learning threshold of 0.7 correct choices, and the total number of choices made by each fish is enclosed in parentheses. Fish J1 was the only individual that failed to learn the cross stimulus.
The eyes of most diurnal reptiles and birds contain coloured retinal filters—oil droplets. Although these filters are widespread, their adaptive advantage remains uncertain. To understand why coloured oil drop-lets appeared and were... more
The eyes of most diurnal reptiles and birds contain coloured retinal filters—oil droplets. Although these filters are widespread, their adaptive advantage remains uncertain. To understand why coloured oil drop-lets appeared and were retained during evolution, I consider both the benefits and the costs of light filtering in the retina. Oil droplets decrease cone quantum catch and reduce the overlap in sensitivity between spectrally adjacent cones. The reduction of spectral overlap increases the volume occupied by object colours in a cone space, whereas the decrease in quantum catch increases noise, and thus reduces the discriminability of similar colours. The trade-off between these two effects determines the total benefit of oil droplets. Calculations show that coloured oil droplets increase the number of object colours that can be discriminated, and thus are beneficial for colour vision.
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doi: 10.3389/fncir.2014.00118 Spectral and spatial selectivity of luminance vision in reef fish
Humans group components of visual patterns according to their colour, and perceive colours separately from shape. This property of human visual perception is the basis behind the Ishihara test for colour deficiency, where an observer is... more
Humans group components of visual patterns according to their colour, and perceive colours separately from shape. This property of human visual perception is the basis behind the Ishihara test for colour deficiency, where an observer is asked to detect a pattern made up of dots of similar colour with variable lightness against a background of dots made from different colour(s) and lightness. To find out if fish use colour for object segregation in a similar manner to humans, we used stimuli inspired by the Ishihara test. Triggerfish (<i>Rhinecanthus aculeatus</i>) were trained to detect a cross constructed from similarly coloured dots against various backgrounds. Fish detected this cross even when it was camouflaged using either achromatic or chromatic noise, but fish relied more on chromatic cues for shape segregation. It remains unknown whether fish may switch to rely primarily on achromatic cues in scenarios where target objects have higher achromatic contrast and lower chromatic contrast. Fish were also able to generalize between stimuli of different colours, suggesting that colour and shape are processed by fish independently.
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Anatomical and experimental data suggesting a slow adaptation of cochlear mechanics are summarized and discussed. All groups of terrestrial vertebrates, possessing advanced hearing—mammals, Archosauria (birds and crocodiles) and... more
Anatomical and experimental data suggesting a slow adaptation of cochlear mechanics are summarized and discussed. All groups of terrestrial vertebrates, possessing advanced hearing—mammals, Archosauria (birds and crocodiles) and lizards—developed intrinsic cochlear specializations, which may adjust cochlear mechanics and therefore adapt hearing to different acoustic environments, or protect the cochlea from excessive mechanical stimuli. Mammalian outer hair cells, several types of supporting cells, hyaline and homogene in birds and crocodiles, and putative contractile cells of the cochlear lateral wall in mammals and in geckos may provide structural basis for the slow mechanical adaptation. Independent appearance of these specializations in animals that developed different cochlear designs may indicate that the maintenance of “mechanical homeostasis” is a common requirement for the highly organized hearing organ.
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Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, foraging and predator avoidance. However, our understanding of animal colour perception is largely derived from human psychophysics, and behavioural... more
Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, foraging and predator avoidance. However, our understanding of animal colour perception is largely derived from human psychophysics, and behavioural tests of non-human animals are required to understand how colour signals are perceived. Here, we introduce a novel test of colour vision in animals inspired by the Ishihara colour charts, which are widely used to identify human colour deficiencies. In our method, distractor dots have a fixed chromaticity (hue and saturation) but vary in luminance. Animals can be trained to find single target dots that differ from distractor dots in chromaticity. We provide MATLAB code for creating these stimuli, which can be modified for use with different animals. We demonstrate the success of this method with triggerfish, Rhinecanthus aculeatus, which quickly learnt to select target dots that differed from distractor dots, and highlight behavioural parameters tha...
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Text file with details of calculations
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SUMMARY Two approaches arc presented lo measure I he qua lily of trichromatic colimi vision oí Hymenopiera in terms of ils suitability lo discriminale bel ween the colours of flowers. Témplales of photoreceptor spec! га I scnshiviiy... more
SUMMARY Two approaches arc presented lo measure I he qua lily of trichromatic colimi vision oí Hymenopiera in terms of ils suitability lo discriminale bel ween the colours of flowers. Témplales of photoreceptor spec! га I scnshiviiy curves are shifted along lhe wüvelengih sui le to search for the optimal set of lliree spectral receptor lypc*. The en lena for optimal ity are: 1, maximal perceptual J i I'leren con between all flower colours; and 2, a maximal number of distinguishable flower colours. We show that lhe set of three ...
Color plays an important role in insect life—many insects forage on colorful flowers and/or have colorful bodies. Accordingly, most insects have multiple spectral types of photoreceptors in their eyes, which gives them the capability to... more
Color plays an important role in insect life—many insects forage on colorful flowers and/or have colorful bodies. Accordingly, most insects have multiple spectral types of photoreceptors in their eyes, which gives them the capability to see colors. However, insects cannot perceive colors in the same way as human beings do because their eyes and brains differ substantially. An insect was the first nonhuman animal whose ability to discriminate colors has been demonstrated - in the beginning of the 20th century, von Frisch showed that the honeybee, Apis mellifera, can discriminate blue from any shade of gray. This method, called the gray-card experiment, is an accepted “gold standard” for the proof of color vision in animals. Insect species differ in the combinations of photoreceptors in their eyes, with peak sensitivities in ultraviolet (UV) and/or blue, green, and sometimes red parts of the spectrum. The number of photoreceptor spectral types can be as little as one or two, as in the...
Evolutionary change is considered a major factor influencing the invasion of new habitats by plants. Yet, evidence on how such modifications promote range expansion remains rather limited. Here we investigated flower color modifications... more
Evolutionary change is considered a major factor influencing the invasion of new habitats by plants. Yet, evidence on how such modifications promote range expansion remains rather limited. Here we investigated flower color modifications in the red poppy, Papaver rhoeas (Papaveraceae), as a result of its introduction into Central Europe and the impact of those modifications on its interactions with pollinators. We found that while flowers of Eastern Mediterranean poppies reflect exclusively in the red part of the spectrum, those of Central European poppies reflect both red and ultraviolet (UV) light. This change coincides with a shift from pollination by glaphyrid beetles (Glaphyridae) to bees. Glaphyrids have red-sensitive photoreceptors that are absent in bees, which therefore will not be attracted by colors of exclusively red-reflecting flowers. However, UV-reflecting flowers are easily detectable by bees, as revealed by visual modeling. In the North Mediterranean, flowers with lo...
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SummaryGaze direction is closely coupled with body movement in insects and other animals. If movement patterns interfere with the acquisition of visual information, insects can actively adjust them to seek relevant cues. Alternatively,... more
SummaryGaze direction is closely coupled with body movement in insects and other animals. If movement patterns interfere with the acquisition of visual information, insects can actively adjust them to seek relevant cues. Alternatively, where multiple visual cues are available, an insect’s movements may influence how it perceives a scene. We show that the way a foraging bumblebee approaches a floral pattern could determine what it learns about the pattern. When trained to vertical bicoloured patterns, bumblebees consistently approached from below centre in order to land in the centre of the target where the reward was located. In subsequent tests, the bees preferred the colour of the lower half of the pattern that they predominantly faced during the approach and landing sequence. A predicted change of learning outcomes occurred when the contrast line was moved up or down off-centre: learned preferences again reflected relative frontal exposure to each colour during the approach, inde...
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Color vision in birds is mediated by four types of cone photoreceptors whose maximal sensitivities (λmax) are evenly spaced across the light spectrum. In the course of avian evolution, the λmax of the most shortwave-sensitive cone, SWS1,... more
Color vision in birds is mediated by four types of cone photoreceptors whose maximal sensitivities (λmax) are evenly spaced across the light spectrum. In the course of avian evolution, the λmax of the most shortwave-sensitive cone, SWS1, has switched between violet (λmax > 400 nm) and ultraviolet (λmax.