| 1. |
- Lind, Olle, et al.
(författare)
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High visual acuity revealed in dogs
- 2017
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:12
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Tidskriftsartikel (refereegranskat)abstract
- Humans have selectively bred and used dogs over a period of thousands of years, and more recently the dog has become an important model animal for studies in ethology, cognition and genetics. These broad interests warrant careful descriptions of the senses of dogs. Still there is little known about dog vision, especially what dogs can discriminate in different light conditions. We trained and tested whippets, pugs, and a Shetland sheepdog in a two-choice discrimination set-up and show that dogs can discriminate patterns with spatial frequencies between 5.5 and 19.5 cycle per degree (cpd) in the bright light condition (43 cd m-2). This is a higher spatial resolution than has been previously reported although the individual variation in our tests was large. Humans tested in the same set-up reached acuities corresponding to earlier studies, ranging between 32.1 and 44.2 cpd. In the dim light condition (0.0087 cd m-2) the acuity of dogs ranged between 1.8 and 3.5 cpd while in humans, between 5.9 and 9.9 cpd. Thus, humans make visual discrimination of objects from roughly a threefold distance compared to dogs in both bright and dim light.
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| 2. |
- Chaib, Sandra, et al.
(författare)
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Fast visual adaptation to dim light in a cavity-nesting bird
- 2023
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - 0962-8452. ; 290:1998
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Tidskriftsartikel (refereegranskat)abstract
- Many birds move fast into dark nest cavities forcing the visual system to adapt to low light intensities. Their visual system takes between 15 and 60 min for complete dark adaptation, but little is known about the visual performance of birds during the first seconds in low light intensities. In a forced two-choice behavioural experiment we studied how well budgerigars can discriminate stimuli of different luminance directly after entering a darker environment. The birds made their choices within about 1 s and did not wait to adapt their visual system to the low light intensities. When moving from a bright facility into an environment with 0.5 log unit lower illuminance, the budgerigars detected targets with a luminance of 0.825 cd m -2 on a black background. When moving into an environment with 1.7 or 3.5 log units lower illuminance, they detected targets with luminances between 0.106 and 0.136 cd m -2. In tests with two simultaneously displayed targets, the birds discriminated similar luminance differences between the targets (Weber fraction of 0.41-0.54) in all light levels. Our results support the notion that partial adaptation of bird eyes to the lower illumination occurring within 1 s allows them to safely detect and feed their chicks.
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| 3. |
- Chaib, Sandra, et al.
(författare)
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Single target acuity is not higher than grating acuity in a bird, the budgerigar
- 2019
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Ingår i: Vision Research. - : Elsevier BV. - 0042-6989. ; 160, s. 37-42
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Tidskriftsartikel (refereegranskat)abstract
- We examined the capacity of budgerigars (Melopsittacus undulatus)to visually detect dark single targets against a brighter background and established their spatial resolution limit for such targets. While the sampling density of the retina limits the resolution of gratings, target detection is theoretically limited by contrast sensitivity. This allows many animals to detect single targets smaller than their visual resolution limit, but this is not the case for budgerigars. The budgerigars were able to detect a high contrast circular target with a luminance profile of a single period of a sine wave subtending 0.065 degrees of their visual field, corresponding to a spatial acuity of 7.7 cycles degree −1 , a measurement in line with the previously measured grating acuity of budgerigars (7.7 and 10 cycles degree −1 ). This result is different from findings on the spatial acuity of humans, who can detect single targets much smaller than predicted by their acuity for gratings. The low contrast sensitivity of budgerigar vision might be one of the reasons why the single target acuity is not higher than grating acuity. Adding a bright surround to the target did not influence detection threshold significantly. However, the threshold was slightly higher for a target with a square-wave luminance profile than for a target with a sinusoidal luminance profile.
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| 4. |
- Chavez, Johanna, et al.
(författare)
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Unexpectedly low UV-sensitivity in a bird, the budgerigar.
- 2014
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Ingår i: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Photoreceptor adaptation ensures appropriate visual responses during changing light conditions and contributes to colour constancy. We used behavioural tests to compare UV-sensitivity of budgerigars after adaptation to UV-rich and UV-poor backgrounds. In the latter case, we found lower UV-sensitivity than expected, which could be the result of photon-shot noise corrupting cone signal robustness or nonlinear background adaptation. We suggest that nonlinear adaptation may be necessary for allowing cones to discriminate UV-rich signals, such as bird plumage colours, against UV-poor natural backgrounds.
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| 5. |
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| 6. |
- Haller, Nicola, et al.
(författare)
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Stimulus motion improves spatial contrast sensitivity in budgerigars (Melopsittacus undulatus).
- 2014
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Ingår i: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 102, s. 19-25
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Tidskriftsartikel (refereegranskat)abstract
- Birds are generally thought to have excellent vision with high spatial resolution. However, spatial contrast sensitivity of birds for stationary targets is low compared to other animals with similar acuity, such as mammals. For fast flying animals body stability and coordination are highly important, and visual motion cues are known to be relevant for flight control. We have tested five budgerigars (Melopsittacus undulatus) in behavioural discrimination experiments to determine whether or not stimulus motion improves contrast sensitivity. The birds were trained to distinguish between a homogenous grey field and sine-wave gratings of spatial frequencies between 0.48 and 6.5 cycles/degree, and Michelson contrasts between 0.7% and 99%. The gratings were either stationary or drifting with velocities between 0.9 and 13 degrees/s. Budgerigars were able to discriminate patterns of lower contrast from grey when the gratings were drifting, and the improvement in sensitivity was strongest at lower spatial frequencies and higher drift velocities. Our findings indicate that motion cues can have positive effects on visual perception of birds. This is similar to earlier results on human vision. Contrast sensitivity, tested solely with stationary stimuli, underestimates the sensory capacity of budgerigars flying through their natural environments.
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| 7. |
- Henze, Miriam J., et al.
(författare)
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An aposematic colour-polymorphic moth seen through the eyes of conspecifics and predators - Sensitivity and colour discrimination in a tiger moth
- 2018
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 32:7, s. 1797-1809
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Tidskriftsartikel (refereegranskat)abstract
- Although predation is commonly thought to exert the strongest selective pressure on coloration in aposematic species, sexual selection may also influence coloration. Specifically, polymorphism in aposematic species cannot be explained by natural selection alone. Males of the aposematic wood tiger moth (Arctia plantaginis) are polymorphic for hindwing coloration throughout most of their range. In Scandinavia, they display either white or yellow hindwings. Female hindwing coloration varies continuously from bright orange to red. Redder females and yellow males suffer least from bird predation. White males often have higher mating success than yellow males. Therefore, we ask whether females can discriminate the two male morphs by colour. Males approach females by following pheromone plumes from a distance, but search visually at short range. This raises the questions whether males discriminate female coloration and, in turn, whether female coloration is also sexually selected. Using electroretinograms, we found significantly larger retinal responses in male than female A. plantaginis, but similar spectral sensitivities in both sexes, with peaks in the UV (349 nm), blue (457 nm) and green (521 nm) wavelength range. According to colour vision models, conspecifics can discriminate white and yellow males as separate morphs, but not orange and red females. For moths and birds (Cyanistes caeruleus), white males are more conspicuous against green and brown backgrounds, mostly due to UV reflectivity, and red females are slightly more conspicuous than orange females. The costly red coloration among females is likely selected by predator pressure, not by conspecifics, whereas male colour polymorphism is probably maintained, at least partly, by the opposing forces of predation pressure favouring yellow males, and female preference for white males. Whether or not the preference for white males is based on visual cues requires further testing. The evolution of polymorphic aposematic animals can be better understood when the visual system of the species and their predators is taken into consideration. A plain language summary is available for this article.
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| 8. |
- Höglund, Julia, et al.
(författare)
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Owls lack UV-sensitive cone opsin and red oil droplets, but see UV light at night : Retinal transcriptomes and ocular media transmittance
- 2019
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Ingår i: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 158, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Most diurnal birds have cone-dominated retinae and tetrachromatic colour vision based on ultra-violet/violet-sensitive UV/V cones expressing short wavelength-sensitive opsin 1 (SWS1), S cones expressing short wavelength-sensitive opsin 2 (SWS2), M cones expressing medium wavelength-sensitive opsin (RH2) and L cones expressing long wavelength-sensitive opsin (LWS). Double cones (D) express LWS but do not contribute to colour vision. Each cone is equipped with an oil droplet, transparent in UV/V cones, but pigmented by carotenoids: galloxanthin in S, zeaxanthin in M, astaxanthin in L and a mixture in D cones. Owls (Strigiformes) are crepuscular or nocturnal birds with rod-dominated retinae and optical adaptations for high sensitivity. For eight species, the absence of functional SWS1 opsin has recently been documented, functional RH2 opsin was absent in three of these. Here we confirm the absence of SWS1 transcripts for the Long-eared owl (Asio otus) and demonstrate its absence for the Short-eared owl (Asio flammeus), Tawny owl (Strix aluco) and Boreal owl (Aegolius funereus). All four species had transcripts of RH2, albeit with low expression. All four species express all enzymes needed to produce galloxanthin, but lack CYP2J19 expression required to produce astaxanthin from dietary precursors. We also present ocular media transmittance of the Eurasian eagle owl (Bubo bubo) and Short-eared owl and predict spectral sensitivities of all photoreceptors of the Tawny owl. We conclude that owls, despite lacking UV/V cones, can detect UV light. This increases the sensitivity of their rod vision allowing them, for instance, to see UV-reflecting feathers as brighter signals at night.
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| 9. |
- Jakobsson, Johan, et al.
(författare)
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Visual cues of oviposition sites and spectral sensitivity of Cydia strobilella L.
- 2017
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Ingår i: Journal of Insect Physiology. - : Elsevier BV. - 0022-1910. ; 101, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- We investigated whether the spruce seed moth (Cydia strobilella L., Tortricidae: Grapholitini), an important pest in seed orchards of Norway spruce (Picea abies (L.) Karst.), can make use of the spectral properties of its host when searching for flowers to oviposit on. Spectral measurements showed that the flowers, and the cones they develop into, differ from a background of P. abies needles by a higher reflectance of long wavelengths. These differences increase as the flowers develop into mature cones. Electroretinograms (ERGs) in combination with spectral adaptation suggest that C. strobilella has at least three spectral types of photoreceptor; an abundant green-sensitive receptor with maximal sensitivity at wavelength λmax = 526 nm, a blue-sensitive receptor with λmax = 436 nm, and an ultraviolet-sensitive receptor with λmax = 352 nm. Based on our spectral measurements and the receptor properties inferred from the ERGs, we calculated that open flowers, which are suitable oviposition sites, provide detectable achromatic, but almost no chromatic contrasts to the background of needles. In field trials using traps of different spectral properties with or without a female sex pheromone lure, only pheromone-baited traps caught moths. Catches in baited traps were not correlated with the visual contrast of the traps against the background. Thus, visual contrast is probably not the primary cue for finding open host flowers, but it could potentially complement olfaction as a secondary cue, since traps with certain spectral properties caught significantly more moths than others.
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| 10. |
- Kelber, Almut, et al.
(författare)
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Limits of colour vision in dim light
- 2010
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Ingår i: Opthalmic and Physiological Optics. - : Wiley. - 1475-1313 .- 0275-5408. ; 30:5, s. 454-459
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Konferensbidrag (refereegranskat)abstract
- Humans and most vertebrates have duplex retinae with multiple cone types for colour vision in bright light, and one single rod type for achromatic vision in dim light. Instead of comparing signals from multiple spectral types of photoreceptors, such species use one highly sensitive receptor type thus improving the signal-to-noise ratio at night. However, the nocturnal hawkmoth Deilephila elpenor, the nocturnal bee Xylocopa tranquebarica and the nocturnal gecko Tarentola chazaliae can discriminate colours at extremely dim light intensities. To be able to do so, they sacrifice spatial and temporal resolution in favour of colour vision. We review what is known about colour vision in dim light, and compare colour vision thresholds with the optical sensitivity of the photoreceptors in selected animal species with lens and compound eyes.
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